found this somewhere on the interweb, used totally without permission and without verifying sources. also i don't know what i'm talking about. but here it is anyway:
The Fit of the Jacket...... 1.\tThe collar should curve smoothly around the back of your neck. About one-half inch of shirt collar should show above the suit collar in the back. 2.\tThe jacket should ride flat on your shoulders without buckling or creasing. 3.\tThe fabric should follow the curve of your upper back and snug into the contour of your lower back. Try on many brands and observe very carefully how each suit fits your back. This can be a tricky area to get, because very little shaping can be accomplished in a center back seam. 4.\tThe lapels should hug your chest, and there should be a happy marriage of shirt collar and suit lapel. 5.\tThe width of the jacket shoulders is critical. Most men buy their suits too large. For a proper fit, the fabric of the upper sleeve should just barely skim the flesh of the upper arm in a suit. The fit of a sports jacket can be looser, but a good dress suit is snug. 6.\tMost men will find a wrinkle of excess fabric below the collar in back. This is caused by having shoulders more square than the suit or by an erect posture. This wrinkle can be removed by pushing the excess fabric up into the collar seam. If this is an alteration you require, make certain that you try on the suit after the tailor has done his work, so you can ascertain that too much fabric has not been removed. Too much will cause the coat to pull outward from the body at the waist and make the suit appear shorter in back than in front. A jacket which has been overaltered and hangs away from the body in back is destroyed. 7.\tPlace the paraphernalia you normally carry into the pockets to check for fit. Few suits can accommodate the volume of stuff that most men take with them. If this proves to be a problem for you, buy a wrist or shoulder bag or a briefcase. 8.\tIdeally, the threads of the sleeve at the upper arm will run relatively horizontal to the floor. Your arm should hang in the middle of the sleeve with approximately the same amount of room in front and in back of it. If your arm hits the back of the sleeve, there will be diagonal wrinkles running from the cap of the sleeve in front toward the elbow in back. Tailors of ready-to-wear do not tackle sleeves. If the sleeves of a jacket you're considering do not hang properly on your frame, look for another suit. Incidentally, this condition seems to bear no relationship to the quality of the suit. It has solely to do with how the sleeve is inserted into the armhole. Sleeve hang could be improved on most suits if cutters would rotate the sleeve slightly toward the front. 9.\tRaise your arms, relax, twist your body and bend to test the fit of the coat. Temporary posture improvement reveals nothing. Stand naturally. 10.\tArmholes should be set comfortably high on a suit coat; on a sport coat, they can be lower. A high armhole allows more freedom of movement than a low armhole. Those in sport coats are set lower to allow for sweaters to be worn underneath. 11.\tSuit sleeves should be hemmed so that they barely cover the wristbones when the arms hang relaxed. One-half inch of shirt cuff will show. Sport coats can be a fraction longer, particularly if you prefer short-sleeved sport shirts. 12.\tThe skirt of a suit should be of ample cut. Vents must be basted closed for fitting so you won't depend on their spreading open to achieve enough girth. The waist will appear slimmer if the skirt fits loosely. Even a slender man will look more fashionable with the slimness accentuated in his midriff and waist by leaving some flare in the skirt of the suit. 13.\tThe length of the jacket should be as short as it can be while still conforming to current fashion. It should adequately cover the curve of your buttocks. The best way to judge good jacket length is to be sure the jacket reaches about one inch below your crotch (not the pant crotch unless the pants are perfectly fitted.) This is more effective than the old "rule of thumb," which assumed all men's arms and thumbs were the same length. * Taken from New Image For Men, Color & Wardrobe by Marge Swenson and Gerrie Pinckney.
hope that helps. /andrew