Modern technology has given us tools that simplify many difficult tasks, but removing hardwood flooring boards isn't one of them. The job is a faster and easier one if you don't try to recycle the boards, but that's a waste of a valuable building resource. Unless the boards are rotten, heavily damaged or worn to the point of cracking, you can use them for a variety of interesting projects or perhaps get money for them from a recycled building materials dealer. Working carefully and systematically to save the wood is usually worth the extra effort.
Removing Floorboards for Recycling
The boards are nailed through the tongues, and the tongue-side of the board is the one you want to pry up. If inspecting the edges of the floor after removing the baseboards doesn't tell you the board direction, look for a row of face-nailed boards along one of the walls. That's the last row that the installer laid, and the tongues should all be facing in that direction. A face-nailed row going down the center of he floor is an exception -- it means it was the first row that the installer put in, and all the tongues should be facing away from it.
You may have to make a longitudinal cut along this row -- or the one next to it -- with a circular saw to make room for a pry bar or chisel to pry the boards out. This means you'll have to sacrifice the first one or two rows.
Wedge a flat pry bar under each of the nails holding a board to the subfloor and pry the nail up far enough to extract it with a pair of pliers. Once you've removed all the nails holding a board, slide the board forward and remove it. Avoid prying boards between nails -- you can easily crack the wood.
Some of the boards will come out with nails still attached. De-nail these boards immediately and stack them to avoid stepping on nails. Similarly, if a nail remains stuck in the subfloor, pull it out before proceeding to remove the next board.
The Express Removal Method
If your flooring isn't worth saving, you can extract it much faster by making a series of wall-to-wall cuts perpendicular to the flooring direction with a circular saw to divide the floor into sections. Use a 24-tooth utility blade and set the cutting depth to the thickness of the flooring plus 1/8 inch. Once you've made the cuts, use a crowbar to pry the boards -- it provides more leverage, and you don't have to bend as far to use it. Use this method to remove glued-down hardwood flooring, which is seldom recyclable.