You should offer 1 year plans if possible. Some people will like not having to renew and you could cut them a small price break.
The most satisfying money you will make as a gym owner will be from members who pay for a 1 year membership, work out a few times in January, then never come back again.
If you decide to offer 1 yr memberships, market hard after Thanksgiving, during the holiday season, and the first few weeks of January.
Here are a few marketing/commercial ideas I thru together extremely quickly:
"A few Thanksgiving pounds got you bummed? Come on in..."
"What better gift to give for holidays than the gift of health"
For New Years, you just change it up a lil bit:
"A few extra pounds you gained over the holidays got you bummed? Stick to your New Years resolution and lose that weight!"
Those were just quick examples, you could probably do better if you took the time to expand on those ideas.
You could also try giving a local women's team or organization free access to your gym. This may get you free publicity, mention in a media/fan handbook, a free ad at a sports arena/stadium, or something similar. Even if the team refuses to do those types of things, they may give you merchandise or free tickets to events. At very least you can advertise the fact that "X Team" works out at your gym.
Co-promote with another business (for example, you could do an ad with local health food store, example radio spot: "after you've worked out and had a shake or smoothie at Jim's Gym (-lol dont know your biz name), you'll want to prepare a healthy meal for you or your family when you home. You can get all your favorite health foods at Mikes Health Mart". You both get an advertisement and get to split the cost. In addition, whenever someone in your gym wanted to know where to get things you may not sell, you could put them to "Mikes Health Mart" and in turn, when people came in wanting to know a good gym or where to work out, they could point people in your direction. You might also want to place circulars (flyers) in that store as part of the agreement.
Never forget that as a business you can still do something merchants did thousands of years ago...BARTER. A local gym I worked at for a while exchanges memberships for all kinds of stuff (oil changes at Jiffy Lube, etc.) A friend of mine was Asst. Manager at the Jiffy Lube and I guess they trade shit ALL the time. They do oil changes for pizza places on delivery cars in exchange for free pizzas & coupons, they've done stuff for donut places, all kinds of shit.
In theory, a membership costs you nothing to create, so if you can trade memberships here and there to others for goods that do have a concrete cost, you'll be making money in a different way.