Step One...

The first step to painting your boat is to take off any hardware that will interfere with the job. This differs with every boat and will be simple for some, and a real pain for others. Suck it up if you're in the latter group! It is what it is.
If you don't remove the hardware, you risk the paint peeling from around it where you've had to mask it off.
Hardware of course includes your toe rail if it runs over the side of the boat, as mine does. I also had to remove my boarding ladder but couldn't remove the stainless ring around the exhaust, and so had to mask that. In these shots, the hardware is still on the transom so that you can see what I needed to do.
Next, you need to remove any wax or debris on the boat's hull. If the boat is dirty, start with a good rinse with the hose, and wipe down if necessary. Then wipe it down with Interlux 202, which will remove any wax or grease on the finish. This is important, because if you sand without this step, you'll grind that wax and/or grease into the finish and it will affect your finish coat's adhesion later on. So wipe it down, it's not a big job. At the same time as you're doing this, note the nicks and other blemishes you'll be filling in later.
Next, out comes the orbital sander and some sandpaper, the grit depending on the condition of your hull. Interlux recommends 220 grit for the initial sanding - because I had a substantial number of dock bites, I went with 120. Since I was using a primer later, I knew I'd be able to sand with 220 then.
If you are not changing the bootstripe, you can mask off the bootstripe now. If you are, you'll have to determine where the new stripe will be, and then mark it in. See this page here.

Nicks and dings - the legacy of 30,000 nm of cruising

Sand the entire hull, and note any dings, high or low spots. These will become obvious as you sand. You'll deal with them in the next step.

Note that I am wearing a dust mask and a tyvek suit. This is a messy job and the dust isn't healthy for you, so take appropriate precautions. For this shot, I took off my safety glasses. And for those of you with eagle eyes, you're right, I'm not wearing gloves and I should be.

In the photo to the left, if you click on it, you'll be able to see it full size. You'll note where I've sanded, to the right side. You can also see a variety of dings, including some wear under the port where a piling rubbed during a storm. That will have to be sanded and then filled and faired.