As a plant breeder, a general rule of thumb:
Choosing the parents is probably one of the most important steps, when making a cross.
Excellent Parent x Excellent Parent -> Excellent Progeny
Ugly Parent x Excellent Parent -> most are Ugly, and the few that are okay, are usually not an improvement over the Excellent Parent
Ugly Parent x Ugly Parent -> almost all will be Ugly
Another rule of thumb, is that when you cross two parents that are "closer" to each other, in terms of genetics your outcome will have a higher chance of being successful, so when you cross say two awarded Maudiae types, you know that your outcome will be good to excellent (more than 40-50% of your seedlings will be "excellent", and the rest of the seedlings are probably still "good" with just a small percentage that may be "duds"), but if you cross say a Maudiae type to a Brachy, you may end up with a lot of "duds". One good thing about these far crosses, is that if something is good, it usually is very good and "different", but the chance of getting a good seedling, may be less than 5%.
And my last rule of thumb (I have many more), is that it is better to out-cross than to self. The only time I ever "self" a plant, is if it is "one of a kind", so if it is truly is way better than anything else (an example would be our awarded tetraploid clone of Phrag. besseae 'Rob's Choice' AM/AOS), or like when mentioned earlier, if it is a rare color form (say an albino form), and it is the only one that you have to work with.
I would say, I have gained my knowledge from experience (I have been breeding orchids now for 12 years), talking to other breeders, reading articles in say the Orchid Digest, and the AOS Orchids magazine, and going to Orchid shows/meetings, like the Paph. Guild the WOC etc.
Robert