First, ask Allah for forgiveness. If you've harmed someone, ask their forgiveness as well. Do tawbah. And then forgive yourself. Don't carry guilt and shame around in your heart like a poisoned dagger. Constant regret for the past is a waste of spirit.
You are not an angel, nor am I, nor any human being on this earth. It's part of Allah's plan that you commit sins, and He forgives you. That's why He has written that His Mercy is Greater than His wrath.
Don't despise yourself. Forgive yourself. It's okay to let go of the past. Self respect and dignity come from who your are right now. You have a good soul, or you would not be here, reading these words.
Tomorrow is a new day. Wake up and thank Allah, and do your best every day. Have faith in Allah's love and mercy, and reflect that in your actions toward others. Be peaceful and strive to be happy.