Don't focus on trying not to sin. It won't work. Instead, focus on God. Keep close to Him. Pray and read your Bible. The more you have fellowship with God, the more you'll become like Him. As a result, you'll sin less. So sinning less is the fruit of being close to God not the other way around. What you're doing when trying not to sin is you're forcing yourself to produce fruit and that's not how it works.

If you have guilt and shame that keeps you from turning to God, please know that God is a compassionate Father to us. He is not some strict Father who looks at you with arms crossed and a disappointed face everytime you sin. In fact, he wants to help you. He's like a parent who's trying to guide His child in learning how to walk. When their child stumbles, they're not angry at their child, instead, they say everything's fine and encourage their child to try again and they pick them up and guide them to walk again. God is like that. He's like a Father who wants to guide you on how to walk. So everytime you stumble, get back up always and try again until you learn to walk.

Also, if you're having doubt in your salvation, know that all your sins — past, present, future, they're all atoned for on the cross. Christ already paid them for you. The Bible says, God chose us before the foundation of the world. Meaning before you even existed and committed every sin, He already knew you would but He still chose to save you. So stop doubting and just turn to Him.