I've developed a few uncomplicated systems that make nearly any upgrade seem achievable. This Instructable lays out these systems in the form of a Hard Drive upgrade.

Begin by backing up your current drive to the one you want to swap in. That way there's no long evenings re-loading Gig's worth of applications and their serial numbers *shudder*

Then, look up the manufacturer of your machine, and look up the support files for your specific machine. Poke around a bit to see if there is a video that explains Hard Drive Swap. If the computer manufacturer doesn't host a short video on it, look for a hard drive vendor that does host hard drive swap info. When you find a vendor that has video instructions I recommend buying from this company. Be fair and support the companies that help you.

Try to find at least two different videos on your subject. Frequently there is better video on one and better spoken instructions on the other. It's just the way it works out *shrug* I dunno.

When you have your video instructions ready watch them repeatedly so that you nearly have it memorized. Make sure you understand any and all terminology and have all the necessary tools. If possible have another computer in a convenient distance (same house is best) so that you can refer to the video if you want. You might also consider downloading the video and burning it to a disc so you don't need to be concerned about connectivity. If possible have someone turn it into a DVD so that you can watch it on a big screen as you work. (As an after thought, you might like to have your cell and the vendors tech service # handy just in case things go really wrong. It's all about being ready for the unexpected.)
Put any four legged friends in another room behind a door, turn off the phones and lower the music volume. It's easier to concentrate then.

Work on a clean towel. This way dropped items don't bounce off the hard surface.
Arrange your tools by kind. All Philips screwdrivers are together, all Torx are together etc
Keep a good supply of Stickey pads or similar next to where the machine is.
Don't spread out all over the place. Keeping things together means they don't get scattered.
Only pick up one tool at a time and when done with it, put it back from where you got it.
NOTICE I live in a humid locale so STATIC isn't an issue for me. You should wear a grounding strap though. They cost about $2 but will save your $2500 laptop from being fried. You can cook electronics with a static charge so small you don't even feel it. It's that old Safe / Sorry thing. Follow the instructions on the package of the strap.

Step 1: Loosen and Then Remove

When the screws are long enough and there are several of them alike, I'll loosen them all and then take them out one right after another that way I can keep track of how many I have moved.
Don't have a screw in your hand when trying to remove a second screw. If you need to catch the second screw you'll drop the first one and the second will most likely disappear as well.
Be Methodical

Step 2: The Stickey Solution

This one item, if you don't remember anything else from this instructable please remember this particular system.
I peel a Stickey off the pad. I turn the Stickey over. Then after I remove the screw from the machine I place the head of the screw into the glue of the Stickey. After I've got all the screws from that particular location I WRITE ON THE STICKEY WHERE THE SCREWS CAME FROM AND HOW MANY THERE ARE.
This alone can pull your bacon out of the fire.
On this particular machine there are over twenty screws with several different sizes and some are Philips head and some are Torx head. As I'd never taken them out it would have been very easy to get the wrong screw in the wrong hole and strip the tiny threads. THAT's an expensive fix.

Step 3: Laying Out the Stickeys

Place the Stickeys one on top of the other as you use them, like shingles. This way you only have to start the rebuilding process from the last Stickey. This really takes the need for imagination out of the equation. It makes this process very hum-drum which, when you're dealing with technology isn't all bad.

Step 4: You're Doing Great-keep at It

It would have been easy to just think that I would remember where those last two screws were or where those two screws were supposed to go.
What I didn't forsee was the fifteen minute fight I had getting the old drive out.

Remember - Murphy was an Optimist.

Step 5: All Done!

That's it? Work your way down through the stack of Stickeys putting the screws where they belong according to your notes. When there's no more Stickeys with screws stuck to them >poof< YOU'RE DONE! Good Job!

Warning - do not dislocate arm patting self on back.

Take a short moment to verify that you have all the tools you started with. I've found pliers, screw drivers, grounding straps and all manner of things on the inside of towers and I've found gum wrappers inside an old PowerBook once so take a look. It's cost effective.