The notion that you need to lift heavy weights when training to see the best results isn't always the necessary path to take in every session. You should try and have different types of workouts in your arsenal ready to use so that your muscles get a variety of training for them to grow effectively. Whilst one style of training is ok to use in my opinion it's optimal for your body to explore different and new ways of training that will not only keep you interested in training, but also allow your body to see increased results.
Lifting heavy weights has it's place and is important when wanting to break down muscle tissue to improve muscle mass and strength, but it's not everyone's go to method of training. It's good to use heavy weights in some of your workouts especially when working on strength and conditioning phases, but then in other workouts you need the focus to be on something else. Here are some good ideas for you...
If for the last several workouts you have been sticking to a specific rep range of no more than 10 reps, then it's time to change this! Exploring rep ranges from low reps to high reps can work the muscle in different ways that you're used to and that is the key here. It's essential in my opinion to continue to mix things up in your workout so so that your body doesn't get used to one outcome. No one ever said you need to stick with a maximum of 10 reps per set to see the full benefits from your workouts and I often range from 8-20 per set. Give this one a try and experience a different type of 'burn' sensation...
Ever tried pausing with a rep when you have the weight and muscles screaming at you? I have, it's a lot of fun (insert blank face here). Basically, what you will be doing is breaking up the reps by having a pause in between the point of pushing or pulling the weight back into you or away from you. Give this one a go during a final dropset or when you don't need to push as heavy, this is going to seriously work you.
Instead of just chucking the weight up and down, really concentrate on what you're doing during each repetition you put yourself through. The focus is nearly always on the initial push or pull phase of the rep but try to concentrate on the negative motion. For example take a bicep curl and the part here to focus on is when you are lowering it back from the top of your chest to the start of the moment. The same goes for a squat, your negative part of the movement will be at the start as you lower and then your push back to standing will be quick. On every negative (eccentric) rep aim to take at least 3-4 seconds before relaxing the muscle.
Give these a go when you're next in the gym, add the ideas to your workout arsenal and you can thank me later when you see the gains ;)