My friend and I plan to visit several clubs before choosing one that hopefully we both like! 

Any pointers please on what constitutes a good Club and good Instructor?

By the way it is an obedience club we will be hoping to join soon.

(Should we join more than one)?

Make sure that the class is not too big, if there are more than 8 dogs there should be a helper.
Have a look to see if they have a syllabus with a clear teaching programme with aims and objectives.
See if they are using kind, fair and effective techniques.
The instructor should be speaking to each owner individually and giving constructive, specific feedback on how to improve, what was good,  etc.
There should be no check chains, physical punishments, etc
The dogs and owners should look relaxed and happy.
The class should be quiet.
If your class is good you may find it unecessary to join more than one, and if you are inexperienced you may find yourself muddled between two or more differing philosophies.
The instructor should be experienced and capable of dealing with different breeds and be aware of breed specific quirks.

Avoid clubs that use a lot of shouting, sarcasm, stomping mindlessly around halls ala sergeant majors and where there is not enough space for dogs to be at a comfortable distance from each other.

you should also feel comfortable and confident in your trainer.
If not then dont join :)