/lit/ guide to learning ancient Greek

'''Which dialect do I start with?? '''

Attic.

(alternatively, Homeric, through Pharr's Homeric Greek)

'''Which textbook should I use?? '''

Most popular options (note I have personally no experience with all but one of these textbooks)

JACT Reading Greek : Well-regarded textbook. (try to get the latest editions if possible)

Athenaze : 2 versions, American and Italian. The Italian is far superior, has much more text and uses natural method more.

Mastronarde: Regular textbook.

Hansen & Quinn: Intensive course. Intended for classroom use, I think.

You can learn with (nearly) any textbook, what matters is that you keep at it.