The basic shrimp escape is fantastic and you should definitely know if but isn't super realistic to get against better and/or bigger opponents. We are going to go over the Step Over Mount escape.
Start with a good defensive frame, elbows tight to your body pushing on the inside of one of your partner's thighs. This will prevent them from advancing their hips any higher. The general idea is to block one of their legs in place with your leg by straightening it out and placing it between their legs, then swing your other leg up and over to the outside of the leg you want to block. Use your heel to scoop up their trapped leg and put it between your legs. If possible, try to put your legs in a triangle around their leg for better control. With the control, switch your hips to the other side forcing their leg up. This space will allow you to shrimp into half guard or even guard if you are slick enough.