In my experience, strength training is about gradually increasing the weight, start with something like 2.5 lbs, then move to 5 lbs as you go. But only add weight once you can do your sets and reps with proper form. Form really matters, bad form is how you get injured.

The other things that make a big difference: eating enough (you need more calories to lift more) and getting enough sleep as well as rest between workouts.

Like every other exercise, it's a question of building a habit.