ACTS 2:38a And Peter answered them, REPENT (change your views and decide to accept the will of God in your inner selves instead of rejecting it).
Essentials 2. REPENTANCE. YOU NEED TO BECOME REALLY GOOD AT REPENTING! - i.e., SAYING "SORRY!" TO GOD FOR ALL YOUR SIN. FACT: The very FIRST instruction given after the Christian Church started was just one single word! -REPENT!! This is so, so serious, and getting it RIGHT will make a major, and completely ESSENTIAL difference in your Christian walk and life.
So just how DO you get it right? First, by understanding what repentance really means: which is changing your mind about continuing to disobey and care little about God and about His daily will for your life! Second, to recognise that all of your sin was and is committed against HIM!! Third, when realisation of a sin comes into your mind, for EACH and EVERY one, earnestly say to the Lord something like this: "I am SO sorry for that sin I committed against You! Thankyou that I'm forgiven, because of Jesus' sacrifice for me! Please help me not to commit that sin again!" You must address each sin individually - just saying (as millions have): "I repent of all of my sins," is simply NOT sufficient, okay!
Fourth is major work for you to do right NOW: you need to spend quite a deal of time going back through your whole life and repenting before a RIGHTEOUS and HOLY God for ALL the sin you've committed against Him. For one reason or another most people will put this off. Decide NOW that YOU will DO it! TWO VERY IMPORTANT NOTES: failure to do this seriously and earnestly will (a) effectively PREVENT you ever living as a True Christian! (b) There will be absolutely no point continuing here until you DO!
Fifth. Spend as much time as you need. You will feel SO WONDERFULLY "CLEAN" when all your sin is repented of! So don't skimp. Don't be slack. IMPORTANT NOTE: once a thing is truly repented of, our astonishing and loving God has forgiven it forever, so it does NOT need to be repented of again (unless you DO it again, of course). God's promise to you: 1 JOHN 1:9 If we [freely] admit that we have sinned and confess our sins, He is faithful and just (true to His own nature and promises) and will forgive our sins and [continuously] cleanse us from all unrighteousness [everything not in conformity to His will in purpose, thought, and action].
Sixth. Now two things as your life moves forward. First of all - maybe sad, but true! - you'll need to continue to repent of sin as you commit it! Then next, you should be asking Him to remind you of more sin. I'm currently 74, have been a continuously serious Believer for 55 years, and - because I've asked Him to - God is STILL reminding me of past sin I've done to hurt and disappoint Him! Do ALL of the above and you've taken about the most MAJOR step possible towards feeling "clean" before a righteous God - AND really becoming and being a True Christian!