I've trained at a few different clubs over the years and been fairly lucky. However there is definitely a few things to bare in mind.
With the surge in interest of MMA there's a lot of places springing up trying to cash in on the scene; we nickname these McDojos. They'll have 6 yet old black belts (no exaggeration) grading every couple of months that cost upwards of £30 a go etc, and will typically want you to buy all sorts of kit. Not that buying kit is always a bad thing - expect to have to buy a Gi (suit) and if you're doing Jujitsu you're best off getting a heavyweight one else they just fall apart. You'll also need insurance but this is only usually about £30-50 per year.
Jujitsu is quite fragmented - lots of different associations with differing styles and outlooks. Some like my own club are purely self defence oriented, no sport leanings at all. Others are very traditional - others more liberal and freestyle. There also the Brazilian flavour which has slightly more ground fighting leanings... So that's something else to consider.
As said the best way to find out about a club is spend a few weeks training there. See what the students are like. Are the higher grades helpful and supportive or are they just using you as target practice? Are there any egos flaring or red mist? How many high grades are in the class etc? How old is the club and how long has the Sensei been training? Who was his master?
I'm really lucky and stumbled across an absolutely fantastic club. The instructor is down to earth and basically doesn't take any **** and will weed out the 'alpha' types - they get bored, give up and go elsewhere. The other members are all great people and despite us lampung seven shades out of each other and often really inflicting a whole heap of pain, there never any intent or malice behind it. It's all done with control, we all have jobs and families to go back to after training and being injured isn't helpful!
In short get stuck in and don't be afraid to try a few places before settling down. Most clubs offer a free first taster session so see what your local area has to offer.
