That's a rather broad subject. There are too many variables at play. Your playstlye, character selection and build, to name a few. At this point I would suggest reading through the UESP Wiki.
The following quote, from another thread, says it very well
At the risk of spoilers, you could visit UESP Wiki (UESP = Unofficial Elder Scrolls Pages) for tips on levelling, efficient levelling, etc. Being that you only bought the game 3 days ago, my recommendation is to avoid all internet help for the first five or six characters you make, and just experience all the playstyles the game has to offer, find the items on your own, do the quests on your own, etc. You will get far more playtime out of the game this way, and come to love it the same way some of the members here do! Happy adventuring!