Generally, it's easy enough following the (sometimes cryptic) instructiuons that come with the towbar. However, I'd add the following tips:
1) If you have to remove the tar-like insulation / sound deadening material from the boot floor, heat it up with a hot air paint stripper to soften it and then scrape it away with a decorator's chisel. Only remove the areas that the towbar will sit on. It's easy to remove when hot and impossible when cold.
2) When drilling the holes in the floorpan (you'll find these pre-drilled and covered with a thinner metal skin) use a smaller drill bit than specified at first and work your way up. You probably won't need as big a hole as specified in the instructions because they seem to be catering for a certain amount of ham-fistedness in locating them!
3) De-burr and paint all holes in bodywork / floorpan with Hammerite. A spray of Waxoyl on these areas once dry won't hurt either.
4) Any securing bolt that passes through a chassis box section (just behind the diff on a saloon, for example) MUST have a spacer fitted to prevent it crushing the box section.
5) Check all fastenings are at the correct torque after first use.
It took me about 1/2 a day to do towbar plus electrics on a saloon.
Kevin