Unfamiliar Openings

The only openings that I really know how to respond to are as follows:

Just play smart. Try to read their offence and mess it up.

Good advice. I will try to take it.

Grandmaster Repertoire - Beating Minor Openings by Victor Mikhalevski.

It is available at Amazon and USCF Sales (under Books --> Opening Books --> Irregular Openings), and I am sure at other specialty shops as well.

After a move like 1.a4 just pretend you're White.

Do you mean like mirroring them?

Thank you. I'll look into it.

Beating Unusual Chess Openings: Dealing With The English, Réti, King's Indian Attack And Other Annoying Systems by Richard Palliser...

https://www.amazon.com/Beating-Unusual-Chess-Openings-Annoying/dp/1857444299/ref=sr_1_1?crid=3GA8KB37GQPM3&keywords=beating+unusual+chess+openings&qid=1581473815&s=books&sprefix=beating+unu%2Caps%2C220&sr=1-1

Taming Wild Chess Openings: How to Deal with the Good, the Bad and the Ugly over the Chess Board by John Watson....

https://www.amazon.com/Taming-Wild-Chess-Openings-Board/dp/9056915703/ref=sr_1_1?keywords=taming+wild+chess+openings&qid=1581474327&s=books&sr=1-1

Chess Openings Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond

No, he means you should take the initiative as if you were white, as a4 is a bad move and does not go for the center.

http://www.qualitychess.co.uk/ebooks/BeatingMinorOpenings-excerpt.pdf
http://www.davidsmerdon.com/?p=1888

https://web.archive.org/web/20140627072813/http://www.chesscafe.com/text/hansen107.pdf

http://www.thechessmind.net/blog/2015/6/30/a-review-of-watson-and-schillers-taming-wild-chess-openings.html

"... Just because a book contains lots of information that you don’t know, it doesn’t necessarily mean that it will be extremely helpful in making you better at this point in your chess development. ..." - NM Dan Heisman (2001)
https://web.archive.org/web/20140626180930/http://www.chesscafe.com/text/heisman06.pdf

Perhaps it would be a good idea to start with Discovering Chess Openings, a book about opening principles.
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

So is this to say that if you want to improve you should read only chess books that contain lots of information you already know?

Ever seen that Venn diagram thing? I would guess that the Heisman idea is that one circle includes books that contain lots of information that you don’t know, and the other circle includes books that will be extremely helpful in making you better at this point in your chess development. The overlap would, of course, be those books that manage to be extremely helpful while containing lots of information that you don’t know. The rest of the extremely helpful region would include books with only some information that you don't know (not lots because of fewer pages or because of more space devoted to explanations, examples, sample games, etc.).

Yes. After a move like 1.a4 Black already has the initiative.

Okay. That makes more sense. But if 1.a4 should I do something like 1.e4 or 1.Nf3?

That's what I try to do. But sometimes I don't know how to occupy the center (e.g 1.a4 or 1.Nf3?)

1...d5, 1...e5, 1....Nf6, whatever helps you controlling the center and developing. Choose a setup you also like to play with White.

1.a4 is really nothing you need special preparation for. It doesn't create any pressure.