As a general rule of thumb, you want to try to avoid buying items off of the auction house when leveling up your first character in Diablo 3. Instead, you want to invest that money into your Blacksmith, as this NPC will be able to create you all the armor and weapons you need for leveling. Not only that, but a high level Blacksmith is able to craft some of the best equipment in the game! You will want to be able to craft this gear at 60, so be sure not to waste your money on Auction House goods which you will out-level in a few hours.
The fact that you level up very quickly in Diablo 3 is the primary reason why you will not want to spend all your money on Auction House equipment. If you buy the best level 10 sword, you will pay a lot of gold for it and then find it is obsolete after a few hours of playing. Save your money and level up your Blacksmith.
Your Blacksmith can create gear for just about every slot (except jewelry) for every class and gets recipes about once every 10 levels. This means you have at a bare minimum a level 5 weapon, level 15 weapon, level 25 weapon, and so on all the way to level 60, just by training your Blacksmith. You get the same thing for armor slots as well.
Your Jewelry needs are easily satisfied by using the first tip mentioned in this Diablo 3 guide â€“ buying from vendors. Vendors often sell rings and amulets and you can always leave and join games until you get the best stat allotments on your jewelry of choice. Between the Blacksmith and vendor-bought jewelry, you should never have to use the Auction House and never have to worry about about gear when leveling up.