The next skill to train easily to level 100 is the Pickpocket. With this process you have save and load often, so if you don't like it, don't use this method. Unfortunately you cannot avoid it, because your maximum chance for the success is 90%. You can use this method anywhere you find a sleeping person. Before you begin the process use the Thief Stone, and sleep at least 1 hour. It helps a lot if you spend 2 Perk points, but it's not necessary.
The method is very simple: smuggle some money to the victim then steal it back. If you have ethical problem, you don't have to frisk anybody. As you getting better, you can raise the amount of money. In this video I trained the skill from level 15 to 100 within 18 minutes. If you intersted in stealing, you should know what is worth to steal. You can't sell stolen items everywhere, only a few merchant buys them. So, I suggest these items: Money, because you can spend stolen money too.
Items made from stolen materials are not stolen anymore. So you can sell them, therefore any raw material. For example: metals, hides, gems, alchemy ingredients, etc. Any magical item what you can Disenchant, for the time being this means every magical items. Or anything else what are you going to use, or somebody wants it and you will give it away. If you finished, you can check the houses and the people in Riverwood, and collect any useful items.
In the next part I am going to show you, how can you easily get the Transmute spell.