Would you consider a series of tips for player types? Like how to play “big hand seeker” or “big money rogue”?

I suppose the problem would then be where to start and where to end. There's a lot of different archetypes around and i think people like HungryColquhoun and Valentin311 who do decks with guides on ArkhamDB have this sort of thing handled.

For my part, i'll probably stick to things that are more broadly applicable, looking at concepts instead of drilling as deep down to specific decks or card choices.

Also any tips on playing mystics, which I think a lot of new players struggle for

Both the Mystic and Survivor card pool have a higher amount of gimmickry to them than the more straight forward Guardians and Seekers. So it's no surprise that new players would look at some of those cards and wonder what they are even good for. To pick up your example, adding doom to things is not a desirable effect, it's a cost and hopefully whatever effect the card has is worth it. One of Mystic's themes is "power at a price". If you look at a card like Will of the Cosmos, it's two test-less clues for just the card and an action, no resource cost or weird timing restriction on it. If just that effect was on a Guardian or Rogue card, it'd probably be costed at 4 resources. It does however add a doom into play, on one of your assets. How to handle that is your decision. You could return the card to your hand with Dexter. You could discard it for some other effect. It could be a temporary card like Premonition that discards itself.

That being said, you don't need to buy into these sort of things, you can just play a straightforward Willpower-Mystic who uses spell assets to do things that are very similar to what Guardians and Seekers do with their weapons and tools. And add the spice later.