Again, you have to factor in how often you are going to get a haircut. What's your maintenance type like? If you want a short haircut, it's going to need more maintenance. After six, seven, max eight weeks, you must trim it because it becomes an image for you. With longer hair, you can get away with eight, nine, 10 weeks at the most.
What gives you the best look for your face? It's what proportion will work for your haircut. If you have a round face, you definitely don't want too many layers around. You want something that's softer for your face and bone structure. You can create some tousled curls, some waves.
It depends also on the type of style you have as well. If you have a long face, you want to leave length on the bottom. Always frame your face; don't completely cut it short along the neckline.