Most importantly find a fitter you know or were recommended to that you can trust. It’s equally as important to see the ball fly, hitting a ball 10 feet into a net and going strictly off of numbers is never a good idea. Trackman or something similar and video are also important.
Have an idea of how much money you want to spend and stick to that budget. Unless you are a scratch to plus handicap player you don’t need all the exotic shafts that may be offered to you. Most companies offer several “no upcharge” shafts that work fine.
Try several companies products and many shaft/head combinations, you may have something particular in mind but find that you hit and like something else better. Have an open mind about what is recommended as far as set make-up. For example you may think you need a 3 wood where a 4 or 5 wood might be much better for you. Get over the ego factor–if you need regular flex shaft but have always played stiff–switch to regular. Stick with the major companies that you know and see others playing–their design/engineering, quality and stand behind product are better than others.
Ask for a print out of what is recommended, unless you are really comfortable with your fitter and their quote do not commit to the sale until you’ve done a little research on cost and what was recommended.
Lastly, take your time if you are unsure about anything go somewhere else and/or hit the clubs suggested a couple more times to make sure.