The basic principle is relative motion. If one object
is rotating another (e.g the earth rotating the sun/ sun is rotating the
earth) it is arbitrary to say which is rotating which. If you are on the
sun you see that the earth is rotating the sun. From our viewpoint on earth
we can see that the sun is rotating the earth. Both perspectives are right.
You could say that both objects are rotating each other. Try it with two cups on the dinner table. Rotate them around each other and imagine what the perspective would be like if you were on each planet." Many people dogmatically state that the geo-centric (earth centred) view has been rejected by modern science, without realizing that there is actually no contradiction just a different perspective on the same phenomena.
When the orbits of the other planets is taken into consideration it becomes a little more complicated. The basic model is all of the planets (including Earth) rotating the Sun, or from our perspective on earth, the Sun is rotating Earth and all the other planets are rotating the sun. Taking the Sun as the fixed frame of references, the position of the planets relative to the sun can be calculated quite simply on the basis of simple elliptic orbits.
Calculating the position of the planets relative to the earth is more complicated, because of retrograde motion. This means that the planets do not simply rotate the earth, but rotate around the earth in a series of loops. This can be demonstrated by keeping one cup (Earth) stationary in the middle of a piece of paper. Rotate another cup around it. (This is the sun.)
If calculating the position of the planets relative to the earth is more difficult, why don't we just use the helio-centric (sun-centred) approach? The reason is simple. We live on Earth, therefore we want to know where the planets are in relation to us on Earth. It is not so useful to know where they are in relation to the Sun. In astrology, it is the position of the planets in relation to us that determines their effect on us.
These are just a few points as I understand them. There may be some minor errors. Check it with the article in BTG and Vedic cosmography. I can send the relevant parts as any attached file if you want. Also there is an excellent multimedia CD-ROM in the pipeline by Sadaputa Prabhu dealing with these very issues. He has advanced a lot since Vedic Cosmography. Some nice comparisons of ancient cultures with Vedic.
I wasn't planning to write this immediately but I got carried away. Let me know if you want any clarification, or if there is anything else I can do for you.