There's several approaches that you can take to interpretation and Astrologers (as in most things)have no simple or unified approach to interpretation.
Basically there are two 'extreme' positions
1 - The Grand Trine has a meaning independent of the planets that comprise it (indeed it doesn't matter what these are, the meaning depends on the element involved. Very briefly the interpretation would be along the lines that you are highly action oriented and continually trying new things. These should come reasonable easily
2 - The pattern has no separate meaning, you interpret the three trines based on the planets and houses involved - i.e. there is a significant difference between Moon, Venus, Jupiter trines, than Mars, Saturn, Pluto trines. There's therefore, no starting point about meaning, each chart has to be judged on its merits.
Obviously there are 'middle' approaches between the two extremes.
For beginners, I would suggest that you start at 2, and learn how to interpret the planets, in their individual trines and taking into account the houses involved. Once you understand that and are comfortable with it, you can try blending in some of the aspect patterns.
One thing you should look for is how much the pattern adds to your understanding, if at all and make your decision whether to use it or not.
