Learn all you can about good horse conformation, from large horse books. Genetics and breeding reference books. Online book stores look for equine breeding management or genetics. There are a lot out there. Then pay attention to as much as possible the dwarfs out there you se, either in person, or on the internet, try to find out as much as possible through first hand info on pedigrees, not, someone heard that such and such stallion had a dwarf or a bunch of dwarfs, when you see them find out pedigree info if possible. Remember what I wrote about how pervasive these dwarfisms are in the breed. Do not get hung up on a certain head type or other individual traits that most likely are not the recessive gene having expressivity. There are a lot of non-desired traits within our breed. We are not a "true" breeding "breed", we can get anything under the rainbow.
John