Go for the regular orbs to begin with, as they do have many staples which are needed for most decks.
In terms of which factions to play to begin with, I’d go for lyonar, as they have some very solid minions to begin with. On the other hand, vetruvian can also be nice as they have access to some nice cantrips, which the basic cards from other factions seem to lack.
On ladder, you will meet many magmar, abyssian and lyonar decks. If you are meeting many magmars, which have a lot of burst, slot in some healing (healing mystic is a nice place to start). With abyssian, board clear and burst are both quite important, and with lyonar just try to gain control of the board.
The main thing that you’ll want to get acquainted with in this game is dispel. Once a minion is dispelled it loses its buffs, as well as all the stats it received. So a 1/1 that got buffed to 4/4 and lost one health after will die if silenced.
As a final note, it is much easier to get legendaries in this game than hearthstone, which is one of the many reasons I prefer it.