Remove all the baseboards around the room or rooms you are laying the floor in with a hammer or pry bar. Unless you plan to replace all of them, take care when removing them so they don't break or crack.
Lay out the recommended underlayment for your chosen hardwood flooring. This is often either a felt vapor barrier or poly-plastic. Allow pieces to overlap 4 to 6 inches.
Choose which way you want your floor to run. Often the floor is laid out parallel to the longest wall or parallel to incoming light, but your personal preference may be something different. To choose, consider laying out small sections in each direction to see which way you like best.
Snap a string line for the first row if the starting wall is crooked. The string line will allow you to lay the floor straight despite imperfections in the shape of the room.
Place the first row, with the groove side against the wall.
Nail the board through the face where it will be hidden by the baseboard.
Nail through the tongue side of the planks at an angle every 6 to 8 inches.
Tap subsequent rows and courses using a scrap piece of wood or flooring.
Pull the last row in tight to the rest of the floor using a pry bar. Nail at the edge that will be hidden by the baseboard.
Replace all baseboards and add transitions and other moldings as needed.