Yay for you! I love my YMCA, my family started a membership when I was about 12 and I liked it so much the Y was the first thing I thought of when looking for a gym membership here. I started out doing the elliptical and the machine weights, doing a full body weight workout and 30-45 min on the elliptical. I did that about twice a week, along with swimming laps and/or water aerobics 1-2 times a week.
I got pretty bored with that quickly, I especially felt the weight machine routine to be repetitive and I just wasn’t seeing progress there like I wanted to after a few months (if you want you can read an exhaustive list of my old lifting routine here
http://www.3fatchicks.com/forum/showthread.php?t=79712). When I started avoiding the gym and missed a few weeks here and there I knew I needed to change something. So I got lots of ideas and support here at 3fc and started trying lots of new things. I’m pretty good friends with the weight bench and dumbbells now and started going to yoga and pilates classes, got some rollerblades, I’ve ordered a stability ball, etc. I just try to add something new to my “workout repertoire” every so often to make sure I’m not getting bored and I challenge my body in new ways.
So my advice: get yourself started, get comfortable, and then be sure to shake it up and try new things! You might be very surprised at some of the activities you could do and enjoy. Have fun!