The first thing you need to do is screw down the sub floor, into the joist, where you hear any squeaks or feel movement. The direction the hardwood will go is not just an aesthetic concern but is a structural one too. Typically, hardwood should be installed perpendicular to your floor joists, so that it is less likely to move between them. If you want to go parallel with the floor joist, then you must build up the floor with plywood first. The overall thickness should be over 1" and be screwed down. Any high spots in the floor should be sanded down with a belt sander. Be sure that the sub floor is clean and dry before you start. Some hardwoods need to be acclimatised before it can be installed. Read the manufacturer's recommendations on this. Avoid storing the material in cold or damp areas like a garage or basement. Use a sample piece of hardwood to cut all of your door casing up to the right height so the wood will slide underneath. You will have to remove doors that are in the way and they may need to be cut down to account for the thickness change.
Many people like to put red rosin paper under their hardwood and the reason for this varies among installers. Some say it helps the wood slide over the sub floor for ease of install, acts as a vapor retardant, stops squeaks, keeps the dirt from coming up through the floor, etc. Read the instructions with the material or consult your supplier and decide for yourself.
Starting the floor is the hardest part of the install. Use a chalk line or laser to get a straight line to start your first row measured off the wall by the width of the hardwood. Most walls are not straight so you may have to scribe out humps in the wall. I like to glue down the first row and pin nail it along the wall and then work out from there. You can use wood glue but a polyurethane glue works better. You will need to glue down in areas that are too tight for the flooring stapler. Follow the flooring recommendations about whether to use staples or cleats to install the flooring. They have their benefits and draw backs for both. When changing directions, you can use a spline. I like to glue and nail it in place.
There are a lot of other issues but that's good enough for now. If this seems like too much for you then do yourself a favour and call a professional. It may save you money in the end.
By Brent Darlington