But the best thing to do is to learn what the sin, cos, and (to a lesser extent) tan and log equations do. These are used loads in this MD presets.
When I have some time, I'll paste some stuff from my various math texts that explains these, and add some commentary. Ryan's guide covers sin() pretty well, at least as far as using it for setting a value to a given range over time, which is what you'd most often want to do in a preset. IMHO learning how sin() works is the single most important aspect of creating "interesting" effects. Read Ryan's guide over and over again until you understand at least that part, if nothing else.
Just a comment: In the context of working with milkdrop, I tend to use multiplication by the reciprocal rather than division when I can. It just seems to me that
zoom = 1 + .1 * sin(ang)
helps to clarify intuitively that you're changing the value by a maximum of .1 Of course x/3 isn't the same a .3*x, but in most cases for working with MD it's good enough, as the computer's only going to perform up to some arbitrary level of decimal percision anyway.
Like 1 + sin(time*rad)/10.
In my experience, what you'll more often want to do is ADD the time, rather than multiply it. Where
1 + .1 * sin(time + rad)
will create an effect based upon the sin of the radius, that changes over time, like a ripple spreading inward/******d.
1 + .1 * sin(time * rad)
will create a situation where the value of the sin wave changes very fast at the outer edge of the screen, and not at all in the middle where rad=0.
It's VERY helpful, even to me, as it gives me a chance to clarify my somewhat fuzzy thoughts on the subject. You have NO CLUE how much I appreciate it.