You first need to decide what it is that you want to fish for. There is no point in joining an expensive syndicate lake with only a handful of large carp in it if you want to bag up on smaller specimens. On the other hand, if you are looking to catch your first 20 or 30, then there is no point in fishing a club pond full of 5lb fish. Funds are unfortunately nearly always an issue, and if they are limited, then you are better off joining a club with several waters or fishing day ticket waters. You don't want to spend out a lot of money joining a carp fishing syndicate that you only fish twice a year. This may all sound rather obvious, but I have known people to complain that they never catch any big carp, when they spend their time fishing a water containing thousands of 5lb fish and nothing else.
Location
Location is also important. Find somewhere that you can easily get to. It can take quite a few trips to a new water to really learn it and understand where the carp frequent, so don't join a water 100 miles from home unless you are sure that you will be able to get there often. If you intend fishing long sessions, then fine, but if you envisage fishing after work for a few hours, then you need a water on your doorstep.
Build yourself up a list of the waters available to you, look out for reports in the angling press and local papers, check out our venues section, and then start to remove any from your list which are too far away, too expensive or don't hold the fish you want to catch. Also look at facilities on offer. Showers, toilets and a shop on site are great if you want to fish weekends or more, or a local garage or shop where you can pick up essential supplies is useful.
Now to narrow the list down. Visit as many of the fisheries as you can. Walk round them. Look at the swims and the access available. Can you park near the fishery? Can you get your tackle to the swims without embarking on a cross-country hike? Is the water so packed with other anglers that the only swim available is almost un-fishable? Talk to the owner or bailiff if possible and to other anglers, although don't disturb their fishing. Find out how well it is fishing and also ask about any fishery rules that may be relevant to you. For example if boilies are banned on the water and you are after catching a big carp, this may put you off.