If you managed to glide the first time you stepped on the ice, you are what is called a "natural."
Seriously, that's all it takes.
You'd be surprised at the number of people who can't figure out a glide, or who fight it when one starts. Here's some tips to getting up a glide on the ice:
Don't try gliding right away. Frankly, if you figure out how to move on the ice, the gliding takes care of itself. A lot of people try to "stroke" (pushing back with the side of the blade) before they've figured out balance, and down they go. This is because they don't shift their weight off the pushing foot. So march, like a soldier. After about 10 marches, just put your feet side by side and relax. You should have built up enough inertia (the tendency of an object in motion to stay in motion) that even though your feet are still, the low-friction surface will translate it into a glide.
There are three types of marches that work: "big" marches, with high knees, fast marches, and loooong marches.
Kids who still can't glide after marching are often stopping the glide-- they'll pigeon toe, or just press down so that they don't glide. Their experience is "if my feet are still then I am still" and so they make that happen. So I'll face a child, take both their hands, and tell them "don't move your feet and don't pull back" and I will tote them like a little wagon, then let go. They already feel the glide, from pulling, so they're more likely to let it happen solo. Once they know what a glide feels like they're more likely to be able to do it from marching.
I don't do this with adults or older kids, because they generally react in one of three ways-- they pull on you, even though you've told them don't. They'll let you pull, but won't let their fee move. Or they'll push you away.
I let beginners push with their toe picks. Yeah, you heard me. This is because it seems so logical. Why else are those things there, anyway? To trip on? Pushing with the toe pick instinctively tells the skater "glide forward." Again, if you're expecting it, it's easier. Plus, toe pushes are an easy thing to fix later.
Not kidding. Of course, you're not really running. You're "fake" running, ice-style. Get down in your knees, bend your elbows, and pretend run three or four or five steps. The second you stop feeling safe, stop "running." You will glide.
A lot of kids get a glide going by subtly letting their legs go wide, in other words, the front half of the swizzle. This is a push and is a perfectly acceptable way of finding out what gliding feels like. The only problem with it is that if you keep pushing out, eventually your legs are going to be really far apart, which looks silly and is hard for a beginner to recover from.
Now do it on one foot.