remember you can increase intensity without increasing the amount of weight..if last workout you benched 100lbs for 10 reps and next workout you bench 100lbs for 12-15 reps you have increased the intensity...
"heavy" is relative..read some of the stickys for training info plus there a few good threads around on things like 5x5 and such..generally you need to keep your reps between 5-12..but experiment and see what works best for you!!
i disagree with this..obviously barring any injuries or nagging pains you should lift heavy all the time..it is diet and cardio that will get you cut!!!
This is a blanket statement that isnt exactly correct.
You can go heavy and do high rep sets. It may be difficult, but you have to trian your body to be able to handle it. However, since genetics plays an important part of lifting, this cant be done by all.
Diet and cardio are critical if you want to be cut. Another area that will help you get cut is if you do high rep sets, like 12-15 reps.