One of the main ways to make your RC crawler grip better is by ensuring that the tires are properly inflated. You can also try adding weight to the front or rear of the crawler to help with traction. Another option is to add a set of shocks that are softer in the front and firmer in the rear, which will help keep the tires on the ground. Finally, you can also add some sort of texturing to the tires themselves, such as spikes or studs, which will help them grip onto surfaces better.