If you really wanna stick to Thief over Assassin, restrain from killing anyone. Instead of stabbing that bandit, wait for him to look the other way and then slip by. Illusion will make this more fun. Also that name is great and very fitting
Instead of stabbing that Bandit, pickpocket him and take all his belongings* Fixed it for you!
You have to think like a Thief. Only take on jobs that are worthwhile. Plan heists out, and I don't just mean Thieve's Guild. Before you put yourself in danger by going into random caves or dungeons, consider whether the treasures within are worth risking your life for. Everything's about getting rich for you. Avoid exploits or easy gold like enchanting iron daggers. Most thieves will avoid murder or killing unless it
absolute necessary, or just an act of self-defense.