Tips on what to look for in a gym?

I think that depends on your budget, whether you have childcare needs, and your goals. If you give more info on your personal circumstances and goals, I bet some of the people here would have some great ideas of what to look for to meet your needs. :-)

weights and excerise equipment, i suppose

Everyone looks for different things. I picked my gym because it has a pool and I like to swim. They have lots of cardio equipment to help me burn cals. They have classes which interest my wife. The weights section doesn't interest me much since I do my lifting at home. It is nice to use the machines for legs though. It is also well kept, friendly atmosphere. A little pricey compared to other gyms in the city, but well worth it to me.

Must haves for me:
Clean and well-maintained
Has equipment/facilities I like to use (ie: if you don't like to swim, you probably don't 'need' a gym with a pool)
Has classes I'm interested in at times convenient for me
Instructors/PTs are trained/certified
Contract terms I can live with (cancellation policies, etc.)

A lot of gyms will give a one or two week free pass to prospective clients. Maybe see if they offer that and try them both. That will help you figure out which one you like. I did that with Anytime Fitness near me before committing to a contract.

Make a list of the important features you're looking for in a gym before you even start to look at what they offer. Many people get sucked into joining a particular gym because once they see that it offers certain things that they never thought they'd need, they suddenly become "must haves" for them. So know what you want in terms of amenities (like pools, tanning, spa items, etc). Also, have an idea of what workouts you plan to do at the gym if possible. No gym has all the pieces of equipment that could be imagined so you want to find one that has the items that are important to you.

When you go look at the gym, pay attention to cleanliness. Also look at the equipment to see how well it is maintained. If cables on weight machines are broken, things are dented, or things just don't appear to be in well kept shape that's a sign. Usually poorly maintained equipment is pretty easy to spot. Also look at how much equipment they have. Do they have a variety of cardio and weight training items? Do they have multiples of the same stations (so that hopefully you won't have to wait for the pieces you need)? Also look around and see how well the place is staffed. Do the staff walk the floor or are they at least easily accessible? Especially if you're new to working in a gym, you want to make sure there are people that can help you out if you need it. Ask a lot of questions about the equipment as you tour the facility. Do this to try and gauge the knowledge level of the staff. Also check to see if they have any type of locker room/changing facilities. Some of the 24 hour chain locations don't always offer this.

Finally, look at convenience/value factors. What are the hours? How close to home/work? Do you get multiple locations or only a single location? Do you have to sign an annual commitment or is it a month-to-month membership? Can you bring guests with you? Obviously, also compare pricing in light of all of this other information and you should be able to figure out what is the best value for you based on your own needs.

Lots of space! There is nothing worse than being cooped up next to super sweaty people (I can't really talk - I get super sweaty too), it is nice to have your own space, with decent areas for weights and nice stretching areas. Also my gym allows me to attend all classes for free, it is wonderful!

I don't have the attention span for machines/weights, so I choose based on the fitness class schedules and convenience of the location.

Barring that: adults-only facilities (or at least where they don't outnumber the adults) are definitely a plus (my closest gym w/ a decent class schedule is unfortunately the YMCA which always has the little brats running around the locker rooms after the pool which also makes the locker room smell like chlorine..since the start of after-work fitness classes coincides with the children getting picked up from school age child care programs).

The best gym is one that you will go to. This is more important than the classes, training, equipment or services. You must be comfortable there - ensure this, then consider issues of convenience in hours, location and specific services of interests.

Personally I am more comfortable in a no frills gym with attendees of a range of ages and fitness levels. But this is not for everyone. What works for you? How do you feel when you walk around? Home or like a fish out of water?

hot trainers to watch.

only somewhat kidding.

SPACE. i hate walking into the weight area and fighting the guys for a little personal space.

Take a tour of each of them, and ask to try it for a few days. Alot of gyms will give you a pass to try for up to a week (mine gives you a 2 week "buddy pass" if you bring in an unwrapped Xmas gift) That way, you can see what amenities are most appealing to you. When I first joined mine I was thrilled with the fact that they had a pool & water aerobics, now I use the pool occasionally but am obsessed with alot of the machines.

Good luck!

I looked at the facility and the members that were there working out. I'm not a big fan of the flashy type gyms Ex: college kids just there to drool all over each other instead of actually working out or professional weight lifters. I am not comfortable in those situations therefore I knew I would not get the most out of my membership. I chose my gym because there were all age ranges there and they all seemed to be interested in getting fit and not making a scene. I do regret that I didn't think about towel service. What sold me on my gym was: attitude of the staff & members, clean, variety of machines, basketball courts, classes offered, locker availability (I live 30 miles from the closest gym), hours of operation, and location. Most importantly I did NOT have to sign a long term contract. I'm strictly month to month. If I want to cancel I only have to give a 30 days notice and there's no penalty when I come back. I typically cancel during the summer because I'm doing other activities. The other flashy gym in town requires a minimum of 2yr contract and their rates are more than double of what I'm paying now.

I looked at the facility and the members that were there working out. I'm not a big fan of the flashy type gyms Ex: college kids just there to drool all over each other instead of actually working out or professional weight lifters. I am not comfortable in those situations therefore I knew I would not get the most out of my membership. I chose my gym because there were all age ranges there and they all seemed to be interested in getting fit and not making a scene.

same here: of the 2 gyms closest to me with classes, one was a "flashy-type" gym full of cookie-cutter blond 20-somethings (it happens to be a female-only gym); the other is the YMCA with more varied women (at least in the fitness classes area) that I liked a lot more. On the other hand, the "flashy gym" offered more classes (they had 2 fitness class rooms instead of just one and neither was shared with spinning classes), a cleaner locker room, and nicer (and a lot more) machines.

Is it convenient for you to go there? If it isn't, you won't go after the first few weeks.
Is it clean? Are the trainers helpful (you can ask a few people this question when you go for your trial workout)?
Bells and whistles: my gym has a pool, sauna and jacuzzi. When I go when the gym is nearly empty, thanks to my atypical hours, I can get a relaxing "spa" experience It's nice. I do this about once a week for a good hour, and often after working out I pop in for a quick 15 minute soak. It's an extra I enjoy a lot.