Step 1: Understand the nature of God’s forgiveness towards you. The teaching on The Forgiveness of Sins is a great teaching to help you there.
Step 2: Repent of your sin(s) if you haven’t already done so. They big key to being forgiven is repentance.
Step 3: Know that your past sins have been forgiven, and that you are now clean in Christ Jesus. Stop thinking about your past sins and start thinking about the new person you are in Christ. We are NEVER told to mull around our past sins, but rather to forget the things which are behind and press forward. (Phil 3:13, “…this one thing I do, forgetting those things which are behind, and reaching forth unto those things which are before.”)
Step 4: Forgive yourself! Jesus made it clear that we are to be forgiving, and that includes forgiving yourself. You need to release yourself from the bondage of unforgiveness. If God chose to forgive you, who are you to hang onto something that God chose to let go of? This is a major source of bondage, and I can’t stress how vital it is for you to release yourself from your past. Colossians 3:13 tells us to be, “…forgiving one another…” If you look up the phrase ‘one another’ in that verse in the NT Greek, it translates to the word Heautou which includes THEMSELF! It is vital to be forgiving towards yourself!! Bitterness (the fruit of unforgiveness), regardless who or what it’s about, defiles a man (Hebrews 12:15).
If a stronghold of guilt exists, then the feelings of guilt may not disappear overnight, because strongholds need to be torn down by the renewing of your mind (Romans 12:2). A great place to start is learning how to recognize condemnation from the devil, and stop paying attention to it. One teaching that will show you how to recognize condemnation is Condemnation verses Conviction.
Once you know the difference between condemnation and conviction and can recognize condemnation when it’s thrown at you, you need to guard your thoughts, and when you see condemnation coming your way, pay no attention to it. Treat it for what it really is… a lie from the devil. You can learn more about how to take control of your thought life in the teaching The Power of Your Thoughts.
If nothing seems to work, you may need to have a spirit of guilt or condemnation cast out. There are particular evil spirits that go around and hang around people like a thick black cloud, constantly making them feel dirty, unworthy and guilty. They usually thrive on strongholds of guilt though, so usually your first step to getting rid of this spirit is by tearing down the stronghold by which it’s holding on. If you tear down the stronghold, and still feel like a black cloud is following you around, I would read the article on Seeking a Deliverance and pursue having it cast out.
There’s a teaching that specifically addresses Strongholds that I recommend reading if you suspect you have one or more strongholds to be torn down.