As a guide line, for upper body movements i recommend 6-10 reps to failure, however if your fail on rep 5 dont worry, you'll get 6-10 on your next workout, and at the other end, if you think you can do 13 reps with a certain weight, don't stop at 10, get the 13 reps, just increase the resistance the next time. For the lower body i recommend slightly higher reps, 8-15 on thigh movements, and 12-20 for calfs. Again don't worry if your off a little.
Of course in some cases, reps aren't even necessary, you can perform static holds on an exercise that provide's resistance in the fully contracted position, examples, lateral raise machine, leg extension, leg curl, calf raise, underhand pulldown, pec deck, preacher curl machine etc, with shorter time under load on upper body movements and slightly longer tul on lower body movements.
Rest period, just enough to allow the heart rate to come down a little, and get your breath back, reset yourself mentally and then get back in the deep end:)
By the way, those rep range guide lines aren't just plucked out of thin air, those are the rep ranges that were found to be the most productive for the given area's by the research of Arthur Jones and his colleagues at Nautilus. Mike Mentzer also used those same rep ranges with every one of his clients (and there were thousands). Also don't forget, in order to add mass to your frame, you need the caloric cement, calories need to be above maintenance level.
Best wishes and good luck with achieving your goals:)