escuan, does this help?
28a - thematic - 7 word for parades + A. Given that this will end "...SA", and if you've got the theme, you can have a decent guess as to what sort of word the answer is.
33a - really mean, I thought. Thematic. First word, in the thematic context, is the definition, and I got it just by googling and reverse engineering the wordplay. X here is a Greek letter.
15a - if you've got the answer, then try feeding it plus "b" and the missing letter into an anagram solver to get a word meaning "watered"
22d - non-thematic! Four letter word for a form of public transport missing its second letter, next to a three-letter vehicle written backwards.
23d - non-thematic. Three-letter word meaning conserve starts it off, which should get you there.
25d - also non-thematic. "The French" is one of the two two-letter words it usually is. Definition is pervert.
Good luck...