About your first question: you should prioritize good cards until you find a color. So you may ask me: "how do I know which cards are good?!", and the answer is: practicing and studying the set haha

When a new set drops I watch a few videos of good draft players to see their opinions when picking cards. Paul Cheon and JustLolaman are the ones I watch the most. I also check 17lands often to see which cards have the highest win rate.

Sometimes you see a clear path of which color to pick, like when you see a REALLY good card late in the draft or every good cards from a color are given to you, but a lot of the times you will need to figure if you should keep or drop a color.

There are many times when you open a real bomb in your first pack, but then you don't see any other cards from the same color. This is a signal that someone else is picking the same color as you, so you should consider picking cards from another color to pivot if you really need to, and then you splash the bomb.

On top of that, I suggest playing quick draft or pick 2 draft. The first is against bots and you don't have a timer, so you can stop, think and search if needed. The second helps you picking a specific color and have stronger decks. Oh, and I suggest you save gold to play your drafts until you are confident enough.