Start slow!!! Don not overdue it starting out. If you overdue it and wake up tomorrow very sore, you will be more likely to not continue. It is human nature to stop doing activities that cause pain (Duh!).
Start with body weight excercises, like pushups, to get into the groove before moving to barbells. Most guys remember what they could lift back in the day and after sitting out 1,2 or 20 years want to start up back close to what they remembered. Bad idea! Start way under where you think you should, better to be way easy and keep with it then to start to hard get real sore and fall off of the wagon.
Anyway good luck
