For a golfer to effectively Troubleshoot His/Her Golf swing the golfer needs a foundation of knowledge.  This knowledge should include:
a.  How His/Her Golf Swing Works (Video is the best)
b.  Basics of a Golf Swing
c.  Golf Swing Model
d.  Ball Flight Understanding
e.  Golf Swing Check List

As the golfer develops and refines their analytic skills of the His/Her Golf Swing, this list will have some additions. 

Golfers should to develop their own Golf Swing Model or Blueprint.  This model or blueprint should be documented and check points identified for reference.  A check point could be an alignment or position of the golf club at a particular place in the golf swing, say for example when the hands are at hip level, the club shaft would be aligned a certain way, the club face angle would be at a particular angle.  Below some check points will be identified that a golfer may find useful.

The DIY Golfer needs a tool kit.  This kit can range from everything such as golf pencils and string to a video camera and analysis software.  Each golfer will over time identify a number of tools that aid in their quest for a golf swing.  These tools are not training aids per-se but tools to help identify what is happening or has happened during the golf swing.

Some of the items one might consider would be:
a.  A mirror or something similar to allow the golfer to monitor the swing.
b.  Masking Tape to be used as club face impact tape.
c.  Powder to indicate lines.
d.  Golf tees or Golf Pencils with some string for alignment.
e.  Video Camera and Analysis Software.

How to Video Record your Golf Swing.  Having a video of your golf swing can be an invaluable aid in diagnosing the alignments, positions, and movements.  Software to analyze your golf swing and compare it to top professionals is widely available.  Some of these packages will suggest how you should set up to video record your swing, you should follow them, in lieu of instruction this topic will provide you with some guidelines.  Click on the link above for set-up information.  The following is some of the software available:

V1 Home Software

C-Swing Software

Motion Coach

JC Video

Swing View Pro

Abbreviated Analysis Method - Analyzing Video and Pictures of the golf swing can prove to be a challenge.  Click on the link above for information on how to analyze a golf swing.

Divots should be taken not only after the clubface has made contact with the ball, but after the ball has left the clubface.  A divot occurs when the leading edge of the club (normally an iron) enters the ground.  This happens because the the golf club is moving downward to the low point of the golf stroke. 

There is no golf requirement that a golfer take a divot and fact is that not all professionals take divots, others only take divots with short clubs, while others will even take a divot with a fairway wood.  Generally a good divot is long, thin and point just right of the target. 

Divot actually has two definitions, the piece of sod that has been removed and hole or bare spot that is left behind.  Note I don't understand why we use a divot tool to repair pitch marks on putting green surfaces but that seems to be the common terminology used today and has nothing to do with this topic.

Most commonly divots occur when using short to mid irons ( SW to 6i), longer irons, hybrids and fairway woods don't normally incur divots, at least not divots that are deep and removing turf. 

So what does a Divot tell the golfer about his golf stroke.

Clubhead Path - The direction the divot is pointing with respect to the Target Line will indicate to the golfer the clubhead path.

- Divot Points essentially STRAIGHT (in reality the proper divot will actually be pointing a small bit right) = GOOD Clubhead Path.

- Divot Points LEFT = BAD Clubhead Path from Out to In.

- Divot Points RIGHT = BAD Clubhead Path too far from In to Out.  (This can also be indicated by the thins shots)

Impact Contact - The location of the Divot with respect to the ball's position will indicate to the golfer the correctness of clubhead contact to ball.  In a proper full golf stroke, the golf club should be moving downward, impact the ball, the ball leaves the clubface and then the club contacts the ground.

- Divot Starts in Front of golf ball = GOOD Clubhead Impact

- Divot Starts Under golf ball = BAD Clubhead Impact, both golf ball and ground struck at same time, sometimes referred to as Hitting it Heavy.

- Divot Starts Behind golf ball = BAD Clubhead Impact, Big Ball (ground) struck before Little Ball, often referred to as Hitting it Fat.

Ball Position should always be prior to low point of the golf stroke which supports the divot starting in front of the golf ball.

The Divot - Divots can come in all shape and sizes and provide a great deal of information about what the golf club is doing. Factors to consider are the Depth, the Starting Edge, the Ending Edge and the Golf Club that created it.

Depth of the Divot can be equated to the golf club that was used to create it.  The higher the loft the deeper the divot will be when compared to a club of less loft.  Depth has a relationship to the golf club's Angle into the ball.  The steeper the angle, the deeper it will be for the same club.  When divots are nothing more than a mere brushing or scuffing of the grass with High Lofted clubs, then Angle into the ball is probably too flat.

Uniformity of Depth of the divot, side to side is another indicator.

- Equal Depth on each side = GOOD Divot, Golf Club On Plane.
- Clubhead Toe side of divot Deeper than other side = BAD Divot, Plane Angle to Upright.

- Clubhead Heelside of divot Deeper than other side = BAD Divot, Plane Angle to Flat.

Starting Edge (closest to where ball was) of the Divot is another indicator.

- Edge Square = GOOD Divot, Golf Clubface is square to the Clubhead Path

- Edge Angled = BAD Divot, Golf Clubface is not square to the Clubhead Path  ( / - open face, \ - closed face)

Ending Edge (furthest from where ball was) of the Divot is another indicator.

- Edge Square = GOOD Divot, Golf Clubface is square to the Clubhead Path

- Edge Angled = BAD Divot, Golf Clubface is not square to the Clubhead Path  ( / - open face, \ - closed face)

Note that the type of grass can effect the actual divot.

CRITICAL - ALWAYS REPAIR YOUR DIVOTS, be it replacing them, using a Sand Mix or what ever the golf course requires.

Divots Rule

1.  You don't have to take a divot for a good shot. 

2.  Good Golfers don't take divots with Drivers when on the Tee Box.

3.  Divots alone can not tell the full story of your golf stroke.

4.  You should avoid taking a divot on the putting green, besides the obvious that other golfers will not be happy, you may discover that the Course Superintend may want to plant a divot on you.  Besides I know Phil M. and you are no Phil M.

5.  The above information does not offer any solution to golf stroke flaws, it only is provided to assist you in understand what the golf club is doing at impact to Low Point of the golf stroke.

Ball Flight

This is condensed form. 

DIRECTION and CURVATURE

Rule #1 – The ball direction will be essentially determined by the clubface alignment.

Rule #2 – The curvature of the Ball Flight is determined by the difference between the clubface and the clubhead path.

There a 9 basic ball flights.  

(#1)Straight – Clubface square to Clubhead path, Clubhead Path square to Target Line
(#4)Push – Clubface square to Clubhead path, Clubhead Path Open to Target Line
(#7)Pull -- Clubface square to Clubhead path, Clubhead Path Closed to Target Line  

(#2)Straight Fade – Clubface open to Clubhead path, Clubhead Path square to Target Line
(#3)Straight Draw – Clubface closed to Clubhead path, Clubhead Path square to Target Line

(#5)Push Fade – Clubface open to Clubhead path, Clubhead Path open to Target Line
(#6)Push Draw – Clubface closed to Clubhead path, Clubhead Path open to Target Line

(#8)Pull Fade – Clubface open to Clubhead path, Clubhead Path closed to Target Line
(#9)Pull Draw – Clubface closed to Clubhead path, Clubhead Path closed to Target Line

Note

- Straight Fade indicates the ball initial direction is close to the Target Line

- Clubhead Path Open to Target Line is an In to Out Path across the Target Line
- Clubhead Path Closed to Target Line is an Out to In Path across the Target Line

It is not uncommon for to hear if the ball starts left, then the golfer has an out to in swing, but this is not necessarily correct.  Look at the divot, look at the ball curvature.

Term Fade and Draw used to indicate the direction the ball is curving.  Normally a Fade or a Draw is considered to be a controlled shot, whereas a Slice or Hook is considered in most cases as uncontrolled.

Trajectory

A number of ball trajectories can occur.

- Normal Flight can be high, medium and low depending upon the amount of forward lean of the golf at Impact along with the Angle of Attack. 

- Ballooning Flight is where the golf ball trajectory starts out normal and then rise up quickly.  This results in a loss of distance and makes the ball very susceptible to the environmental elements.

-  Other trajectories can occur, the skulled shot (ball on ground), the topped shot (ball bouncing on ground a short distance), the shank shot (ball goes sideways from direction club is moving), pop-up shot (flies high and short), etc.  All of these shots are a result of a poorly executed golf stroke.

Trajectory control is a function of the golf club.
1.  Clubface Loft
2.  Forward Leaning of the golf club shaft
3.  Angle of Attack