Friedrichshafen has always had a certain level of interest with anyone who is passionate about flying, as it is home of the Zeppelin.
For a long time, the only regular flights to Friedrichshafen from the UK were operated by Ryanair from London Stansted. Although these have since been halted, Monarch have launched new flights to Friedrichshafen aimed at the Winter 2012 ski season. The leisure airline will operate flights from Manchester as well as from Gatwick.
Additional flights to Friedrichshafen may be available as part of a ski package.
Despite being a relatively small airport, Friedrichshafen airport has its own railway station adjacent to the terminal, as there is a local line passing right next to the airport site. The transfer into the centre of Friedrichshafen takes just six minutes.
Outside the ski season, it is much easier to get to Friedrichshafen by flying in to another major airport nearby, rather than trying to take connecting flights, which are few and far between. The most obvious option is to look for flights to Munich first, especially as a good range of leisure and network airline flights are available to the Bavarian hub.
For once, Ryanair's version of "Munich West" might actually be even more central, as their alternative Memmingen airport is actually closer to Friedrichshafen than it is to Munich. A small selection of flights to Memmingen is available from a handful of UK regional airports as well as from London Stansted.
When Ryanair still operated the Friedrichshafen route, we advised that this could also be seen as a cheap alternative to flights to Zürich, especially as the Swiss financial hub was very hostile to low-cost airlines at the time. Now, we would simply advise doing it the other way around -- if you want to get to Friedrichshafen or anywhere around Lake Constance (especially during the summer), why not fly to Zürich first and then transfer by road or rail to wherever you are trying to get to.
There are also plenty of ferry services operating across Lake Constance itself, and this should make for a very pleasant trip if you have the time to enjoy it.