well I am an electrician... they key to success in this project is 2 things:
1: having an understanding of tools and how they are used, and basic construction/ remodeling skills. I say this because too many times I have had to bail out homeowners that do DIY projects and dont realize what they have gotten into and tear something up in the process. ex: a guy i helped out after he cut into his service entry cable when drilling a whole to get some 12/2 into his panel. the moral of the story is plan careful, check 3 times, and have an idea of what your getting into BEFORE you start.
2: a good understanding of how power works and why things have to be the way they are. alot of people assume that when with dealing with electricity, as long as it works, its ok and safe. this is not always the case. usually the only warning you get (besides breakers trippping) is the smell of your house burning. also you have to understand that wires ar elike pipes, they carry only so much power before they fail,(like a pipe will burst if theres too much pressure) so you have to take into account your existing power requirements, the size of your wires coming in from the street, the amount of new power your going to need, and then see if your service from the street is actually big enough to handle the additional load. this is critical...
a key point to remember here: alot of people tend to go and look at something that works, then duplicate the connections on the device they are installing. you cannot do this with a sub-panel. here's why- in your main panel, the neutrals and grounds are connected together or share the same terminal bus. this is called bonding. im not going to go into why this is done, but its something that HAS to be done. but only @ the main panel, never in a sub panel. i cannot stress how important this is, because if your subpanel is bonded, then the frames of everything you have connected to your electrical system will now be energized.....
keeping those things in mind, installing a sub panel is not that difficult at all, running the wire is the hardest part