Size wise depends on height and weight..... Also your type of riding matters. Im 5'11" between 160-175 depending on how active ive been lately haha. For my All mountain board i ride a 158 (Burton Custom). My Park board is a 156 (Burton Twin). Now that ive gotten a little fatter than when i bought the 158, id probably go with a 160 next time. Longer boards help "float" better in powder. For example my 156 park board is much more flexible and shorter, so if i get in some deep powder, ill be riding along and all of a sudden it will just nose dive if im not all the way on my back foot.
Also what size shoe do you wear? Supposedly a boot size of 10+ and you need to start looking at Mid-wide - wide boards to avoid toe drag. Cant really go by your shoe size either. I wanna say that I wear 11.5-12 in Nike Dunks & Shocks, and a 10 in Salomon and Burton boots (due to the packing out that boots do).
Try Burton's Board Finder
http://www.burton.com/on/demandware....oardFinderShow
It should give you an idea of range, although i wouldnt go with the boards they recommend, because the first ones are normally gonna be their most expensive ones $700-1000, but it should give you a length and width to be looking for.