Deciding on flavor is a preference of personal taste. When you're looking for one, my recommendation is to try to get small amounts so you're not wasting money until you find something you like. Try not to get caught up in building a collection of eJuice you're never going to use

It's fun to try different flavours but you are switching from regular cigarettes and want to make the switch successful, you really need to find some that you can consider an all day vape to replace your regular cigarettes.
This is purely high level, Ejuice generally consists of
Propylene Glycol (PG)
- Will Give you More Throat Hit
- Thinner Liquid so more PG will give you thinner liquid
- Can Dry out your mouth and some people of issues with too much PG
Vegetable Glycerin (VG)
- Will Give you more smoke, and one or more combinations of ingredients to make up the flavor.
- Will give you more smoke
- Thicker Liquid, makes your ejuice thicker which can affect performance of some setups with higher amounts.
- Sweet so gives a little sweetness to your flavours (not a bad thing)
Flavouring
- Can consist of multiple ingredients to add flavour
The standard ratio thends to be 70%PG/30%VG. A lot of people seem to find this a good combinations. Myself personally, I find with heavy vaping, my mouth dries up and I get soreness from vaping too much PG. I like a 50%PG/50%VG mix, I think it's a better start for most people because you can move from there. Want more throught hit, up the PG, want more Vapor, up the VG. Of course the results vary from ejuice to ejuice and flavoring especially if it includes water can also have an effect and some flavouring can simulate that throat hit without additional PG. You might like one flavor at 50%PG/50%VG but you might like another better with a different combination. This information should give you an idea but really it when it comes down to it, it's personal perference. Some people like the 70/30 combo, some people like 50/50 and some just plain like 100%VG. Just buy small bottles, give them a try and find your perference on your favorite liquid.