The thing to keep in mind when packing is that, to a certain extent, you’re doing more than packing. Packing is pretty much the only time you deal with all your stuff at once, and so it’s also a time for evaluating your stuff.
Others have mentioned that you should have divide stuff into three groups: Stuff you want or need, stuff other people might want but that you don’t (good will, things you’ve borrowed but haven’t given back), and garbage. Deal with each as appropriate.
I disagree with the idea of mixing books and clothes and so on. I like to have only stuff that goes together in each box, which I can then put close to where it’s going to end up. This, in the end, saves me from having to wander from room to room putting things here and there when it’s time to unpack. It also helps me figure out stuff that I need but that I don’t have. (For example, I’m not good at keeping track of scissors, for some reason, so if I don’t see them in the “office” box, I don’t have to wonder if they’re in the “kitchen” box or who knows where else. Use smaller boxes for books.
Pack everything with a lot of packing paper to prevent damage. Protect the corners of furniture, at the very least.
Other than that, I suggest packing from the inside out, in a sense. Start with closets, cabinets, drawers, and the like. Then move from most to least used. If you don’t cook all that much, pack the kitchen before the living room. Or vice versa, if you don’t spend too much time watching tv, you might want to pack the living room first. You get the idea. Stack boxes as they are filled somewhere reasonably close to the door. If you have a dining room, it’s usually ideal. Just pack the table and you have lot of space.
Generally, the bed, necessary bathroom stuff, and food is last. Put the bed linens, as well as clean bed linens, toilet paper, a bar of soap (unpacking is dirty), paper towels, and a couple changes of clothes, including pajamas, in the “open first” box. I tend to use a suitcase or two for these things, since you don’t need any tools to open it, and even if it gets lost in the truck somewhere, it’s easy to pick out. Perishable food can go in a cooler. If you’re not moving far, don’t bother with ice. If you’re moving pretty far, just give the food away. It gets to be a pain.
I like unpacking. I like to see the dull brown of the boxes mix with the brighter, better colors of my stuff and watching my new place take shape. Finally, if the new place isn’t clean, clean it before unpacking. It’s pretty much the only time my place is exactly like I want it, before real life sets in, and I don’t have the time or the desire to move everything before I wash the floor (or whatever).