Ganesha's seed mantra is Gam, and verses 7 - 9 of the Ganesha Upanishad comprise a simple meditation upon it. A basic meditation on a bija mantra can be performed by intoning it whilst meditationg on the Devanagri character which denotes it. However, an intimate knowledge is difficult unless one has a basic knowledge of of the Sanskrit language. Mandalas and yantras are geometric symbols. Again, a large amount may be gained from merely meditating in the symbol, and seeing what pops into your mind.
All ideas are valid.
Success can be gauged by the coherence of the different ideas with each other and whatever else is known about the deity. All lines of thought are useful, even those which lead to a dead end. A good analogy is with a vehicle maintenance manual translated by a mechanic rather than a linguist. The latter may have a greater skill with word, but the former will actually have performed the procedures. The final symbol is the rupa , or form of the deity.