Where you are at right now you can probably go up every workout so long as you dont start too high. You want to be making progress every time in the gym so you either want to increase reps or weights. Lets say you do 3x5 this week then next week either go up 5 pounds and shoot for 3x5 again or do the same weight and try to get 3x6.
There is a routine on the bb.com forums where you pick a weight and use the same one for 5 weeks going up 1 rep a week from 5-10. Once you get 10 for your 3 sets you increase the weights and start over at 5 then repeat.
Just make sure whatever you decide to do stick with it for a little while before you change things up. So many people get training ADD and keep trying to change something before letting the first thing actually work.