Well, eat about 300 calories above your daily recommended amount. This way you will be gaining muscle more then fat. Eat healthy, nutritional food (almonds, fish, chicken, pasta - the list goes on). If you are bulking you are bound to gain fat, but if you do cardio throughout the week you will gain more lean mass.
A good way to tell if you are having good gains if it you are gaining about 1 pound every week. Any more and you are gaining to much fat. If you aren't gaining enough, simply up the calories by 100 or so.