Fairway woods deserve more attention than they usually get from most golfers. You hit them off the tee on a long par 3 hole, and sometimes on the longer holes when your driver won't cooperate. Long par 4 holes and most par 5 holes are where most amateurs pull out a fairway wood to reach or get close to the green on a good line of approach from the fairway.
Considering all the shots during a round where a fairway wood is the best club for the distance ahead, most golfers treat fairway wood fitting as an afterthought. And that strategy usually leads to bad choices based on questionable information. Fairway wood fitting is important to your game.
Most fairway woods off-the-rack are too long. A half inch difference in shaft length has almost no effect on distance achieved but it can have a major effect on efficient contact with the ball. Start by getting club length correct.
Which fairway woods should you have in your bag? Woods that you can hit easily to get the ball in the air with a higher launch angle than you get from the driver. You want the ball to land softly on a target for distance control. For most amateurs that means forget the 3-wood. If you have one, leave it at home unless it serves as your driver. Professional clubfitting will help you make the right choice of loft, shape, clubhead design, etc.
Shaft flex and shaft weight is where most golfers get poor advice. Your best approach is to think about what you want the fairway wood to do -- get the ball high in the air with an easy swing that doesn't feel like work. That means optimizing flex and weight for your swing style and the weight of the clubhead. The shaft will be softer and lighter than you would otherwise consider.
It's not uncommon to decide on a different brand or model than the driver shaft, as well as a softer flex and lighter weight than most retail recommendations. The fairway wood swing is not the same as the driver swing, consequently there is no reason to apply the same shaft fitting strategy to both clubs.
Premium upgrade or aftermarket shafts are usually your best choice for fairway woods to get the ball trajectory and control to bring these clubs to life. You will appreciate a properly fit club when you are standing on the tee of a long par 3 hole and need to hit the ball over a nasty hazard and onto a green protected by deep bunkers and deep rough.