How do you remember the case for a certain noun? I don't find 'an doras' (m) or 'an deise' (f) useful at all. I prefer using the genitive case with the article, and I'll add a verbal noun to it:
doras, fosgladh an dorais
- an = masculine
deise, cruth na deise
- na = feminine
This way, I even get 3 for 1:
- the gender of the word
- the genitive form of the word
- a useful expression