A good professional club fitter will test the following seven interrelated variables during a custom fitting session: shaft length; lie angle; shaft flex; shaft type; grip size; golf club head design; and set make-up. Each variable is briefly explained below:
Shaft Length:
Among other things, shaft length will impact where on the clubface the ball is consistently struck. The correct shaft length will prevent a golfer from having to alter a natural swing arc in order to make an optimal impact.

Lie Angle:
This is the angle formed by the shaft and sole of the club. Having a correct lie angle will cause the center of the clubhead to touch the ground. If the toe of the clubhead is raised, a hooking shot may result. Should the heel be raised, a push or slice may result.

Shaft Flex:
The shaft flex impacts things such as trajectory, accuracy, distance, and consistency. During the golf swing, the club "flexes" throughout until squarely meeting the ball at impact. An incorrect shaft flex significantly reduces the chance of making consistently solid contact.

Shaft Type:
Here, again, personal characteristics make the decision. The composition of steel and graphite shafts, their kick (or bend) points, swing weights and torque ratings are considerations

Grip Size:
The right grip size can impact the golfer's ability to return the clubface to a square position and release the wrists through impact. Also, with the variety of grip compositions, personal preference is a determining factor.

Clubhead Design:
With the advent of MOI (moment of inertia) importance, this factor has become a big consideration, particularly with higher handicappers. When shots are struck outside the sweet spot, a high MOI reduces twisting at impact, delivering shots closer to the target area.

Set Make Up:
The new hybrid clubs have given golfers a wider range of choices in the clubs they carry in their bag, their set make up. Numerous lofts and designs in woods, hybrids, irons and wedges make the need for professional custom club fitting more important.

Due to the interrelatedness and number of variables, it is difficult, if not impossible for anyone aside from a professional to conduct a proper club fitting. Online golf retailers offer club fitting, but often all factors aren't considered. Club fitters should be able to give golfers personal attention and many often use technology in the form of launch monitors as one means of assessment. 

A launch monitor typically measures clubhead speed, ball speed, launch angle, spin rate, carry distance and overall distance. Measuring these characteristics, along with others, will help the club fitter select the proper clubs for each golfer. Many golf shops will offer club fitting without requiring club purchase, albeit for a fee. 

After a custom club fitting, golfers will feel confident that they have made a good decision on their investment. The added confidence will enhance performance almost as much as the custom fitting itself. 

I'm just starting out...I'm not good enough for custom fit clubs. False, You probably aren't as good as you can be! 

I've been golfing for a while, I don't need to be fitted.
Maybe not, but depending on the brand you have been using and perhaps taking into consideration some physical attributes you should be re-fit before buying another set of clubs.

I don't need to get fitted in person, I can do it over the Web! 
Not all measurements are those that can be gathered by yourself. The Custom Fitting process is broken down into 2 distinct phases: Static and Dynamic. Some of the static measurements you can obtain yourself, but the dynamic fitting is where your natural form is analyzed under the keen eye of your skilled fitter to determine the "your" clubs! 

It is more expensive to have clubs custom fitted.
Actually, not true. Mizuno charges you no more to create you "your" perfect equipment. You may be charged a fitter's fee but most likely this can be applied to your new purchase. 

Custom Fitting takes a lot of time and will delay my order.
Definitely not. The actual fitting can take anywhere from 20 minutes to several hours - depending on how long it takes the fitter to collect all the information. Once all the information has been obtained by us your new set of clubs will ship out between 5 to 10 business days. 

Club fitting will take into account several characteristics of the golf club when determining which club setup is for you. The main ones are as follows:

Length of club 
This is very important on a couple of levels, one is that you want the proper length club so that you feel comfortable with it in your hand. You won't feel the need to choke up on the shaft or feel like you are reaching for the ball. The proper length of the club also lets the club maker assemble your club to have the correct flex in the shaft. If you choke up on the club you are in essence moving the kick point which in turn stiffens the shaft. Think of a telephone pole, when the pole is long, it can sway in the wind, cut it shorter and it is extremely stiff. 

Loft issues
For some players, loft fitting becomes a factor. If you hit the ball too high, you may be told that you need stronger lofted clubs or low trajectory clubs, if you just don't get the ball up, you may be told that you need higher trajectory clubs. This is more of an advanced kind of fitting as most clubs can't be adjusted this way, they have to be cast or forged strong or weak. Some companies offer lines of clubs this way, usually designated as pro versions for a lower trajectory, or ht for higher trajectory. 

Grip fitting - The size of the grip is important if you have very big hands or very small hands, or arthritis or some other medical reason that needs to be addressed. This is usually determined by your glove size.

The Size is the most important factor to consider when choosing a grip. The wrong size can affect the directional outcome of the shot. Too small a grip could promote pulling the ball, and too big a grip could promote a slice. 

There is no exact science to fitting a grip. However, it is generally considered by clubmakers that the fingertips of the upper hand should just be touching the pad of the upper hand whilst holding the golf club. Other considerations to grip size could be arthritis or tennis elbow where a larger grip would be fitted to aid gripping. 

As well as standard, midsize and jumbo grips from manufacturers, custom sizes can also be achieved with the use of build up tape under the grip. A size change of as little as 1/64" can be made by the clubmaker. 

Grips also come with differing inside core diameters, the usual being .580" and .600". If the core size does not match the butt size of the shaft, this will also change the size of the grip.