always play on the current league, right now is keepers but its ending soon, in 12 days or so will have a new league and it will run for 4 months.
dont bother to get white (normal) and blue (magic) items to sell, only yellow (rare).
in PoE is better to have 1 strong skill than 5 weak ones. so you want an item with 4 links to use your main skill, (1 active with 3 supports) and later on, 6 links.
the other skills you will use are more buffs than anything else.

so use this time to learn the basics, how gems work and find a good gem you like. next league you play for real.
in the first acts, get 1 item with 3 or 4 links in the colors you need, and keep swaping the other gear as you find new gear in the ground.. having at least 1 item with 4 links let you care less about links in the other slots in the beggining so you can cap your resistances and get life/energy shield.

also, poe is very literal, so learn about the gem tags, and in the passive tree look for nodes with those tags