Bathrooms can be harder to do than kitchens. Generally, the space is smaller than a kitchen, but many of the same factors come into play. Attractiveness of the floor is always very important, but there are other considerations that are just as important.
Measure carefully: A bathroom is going to be fairly easy to measure. Just measure the entire usable floor space (not from wall to wall, otherwise you'll include the tub and shower space), subtract out the size of the cabinets. Order about 10% more than you need for overages.
Durability: This is a high-traffic area, so a high-traffic solution is in order. This floor will probably take a beating, so choose a flooring that can handle it.
Moisture-resistance: Water is the enemy of your home's structure. That makes wood or laminate flooring a poor choice in this case. Consider tile or linoleum, or any product that is water proof and can withstand frequent mopping.
PRO TIP! Be aware that there may be a surprise or two in store for you when you remove the existing flooring. Look for water damage in the subfloor, for areas of mold or water stains. Walk all around the room, stepping hard and purposefully on the subfloor. If there is any sponginess, that subfloor needs to be replaced. Just covering it up could result in this flooring job being a waste of effort. If the subfloor needs replacing, don't be afraid to hire that work out. This is harder work and a pro has the tools and experience to do it quickly and well. The money you "save" by doing this yourself may be wasted when you mess something up.
Build-up for flooring: You'll need to plan for a layer in between the subfloor and your flooring choice. For tile, you'll need backer board. This gives you a surface to spread the thinset adhesive. For linoleum, plan on a layer of 1/4" lauan plwood and a floor-leveling compound. Any bumps or inconsistencies in the floor beneath the linoleum will only be magnified after installation.
Fixtures: Plan on removing the toilet for the floor installation. Working the flooring up to the base of the toilet will make for a poor visual fit. It would also compromise the water-resistance of the flooring, leaving a perfect entry point for moisture.
Trim and baseboard: Plan on pulling the trim from the wall, and lay the flooring in below it. Then when you replace the trim, there is no risk of gapping.
PRO TIP! To remove trim without damaging it, cut carefully along the caulk line that ties the trim to the wall. Then slide a putty knife in behind it and gently ease it off the wall. Be careful that you don't put a hole in the drywall.
If all goes well, you should be able to reinstall the trim, caulk it to the wall again, and paint. Just be aware that sometimes the trim breaks, even for a professional. Care and patience are your best friends for this task.