Two pieces of advice for now.
This first piece has been a doozy for me and I had to learn a lot of things the hard way. Pay attention to your coordage! Not all strings are created equal.
I learned a lot of my knot tying using cheap clothesline. It was cotton finely braided around a core of nylon. I got used to using it, how it felt, and how it knotted. A lot of those knotting tricks did not translate so well to 3-strand twisted nylon. The nylon was a very different kind of beast - not just in fiber, but also in that it was twisted instead of braided over a core.
If you need strength, go with a synthetic. If you want skin friendly (bracelets), go with natural. Not only do they feel different when worn against the skin, but they also knot very differently. Natural fibers tend to have more friction and require less knot work. Synthetics tend to be smooth and slippery and more care has to be taken.
If you were to do a macrame belt with nylon, I'm sure it would look pretty. However, there is a chance that the knots will collapse or re-dress in certain areas if too much force is applied. Or if design and knotting isn't the greatest. I'm not saying that it can't be done, but care should be taken.
Also notice how the yarns were put together to make the final rope or cordage. I've had a few bad experiences trying to untie twisted rope that had gotten too tight. If given the choice, I'll take braided.
And then there is rope with a core. I have actually braided some of this myself. Strong nylon in the middle and soft hemp on the outside. Best of both worlds - mostly. One problem you may run into with cored rope is slippage between the core and the sheath. I've lost a decent measure of coordage because of slippage and sheath stretch.
I'm crazy and I have all sorts of strings, yarns, and ropes all over the place. All pros and cons for a given task. You don't have to get crazy, of course, but pay some attention.
My other piece of advice is learnnig how to whip the ends. A regular over-hand knot will work dandy in most cases. But sometimes it will take more than a simple knot to keep your ends from fraying too much. With nylon, I prefer electrical tape and melt. I know a guy that whips his nylon with regular nail polish. For solid braids, I prefer a half-thistle knot. Some use needle and thread. Still others prefer a hot glue gun.
For the most part, I will use a regular over-hand hand knot to start. When I'm finished doing whatever it is I am doing, then I'll worry about finishing the ends. The over-hand knot being a place-holder of sorts until it is time to get serious about finishing.
With that said, do some playing, pick a direction, and I'll do some navigating.