You know how practice makes perfect, and using muscles builds muscle? It’s the same way in the kingdom. The more we extend our faith, the stronger our faith gets. You may start out only able to believe for small things, but as you see God respond to that little faith, it’s easier to believe for bigger things.
In the same way, the more we resist the bad thoughts of the enemy, the easier it is to resist them. Once you realize that bad feelings and bad thoughts don’t come from God, you can make up your mind to not receive them. You can literally tell yourself to ignore them. Claim the good things of God and the enemy will have to leave you alone.
You may need to remind yourself to do this somehow. Just remember that anytime you’re feeling bad about something, do a check. Where is it coming from? Is it something you did? Repent if you need to, God forgives. Is it coming from someone else? You don’t have to receive it.
The more you guard your heart, the stronger you’ll get. The more you resist the enemy, the more of God you can claim. It’s like taking enemy territory every time you refuse to be unhappy.