I should have a full guide up soon, but this’ll suffice for now.
Mulligan for Explosive Trap, Snipe, Phase Stalker, Mad Scientist, and Pack Tactics against Aggro. Against Control, keep Phase Stalker, Cat Trick, Dragonsbane, Rinling’s Rifle, Manafeeder Panthera, and Scavenger’s Ingenuity.
Zul’Jin is a bailout option, and he sets your Hero Power to a 2 mana that’s aimable. Don’t use him unless you need to. Usually, he puts up a Christmas Tree of Secrets, draws a Beast or two, does damage randomly and perhaps draws a card with Quick Shot.
Play Snipe before a minion your opponent will want to keep is likely to go down. Nobody expects it. It’s easy to win games off of Waker Mage by Sniping their Wakers or their Stargazer Luna. Murloc Shaman really hates losing their Firemancer Flurgl, Underbelly Angler, or Warleader. Plan for Snipe to go down a turn before a strong opposing minion is likely to, and don’t use it willy-nilly unless you’re against a Waker Mage.
Wandering Monster, Freezing Trap and Explosive Trap can be combined in unexpected ways. Remember that if Freezing triggers before Explosive, Explosive won’t damage the attacking minion.
If you intend to play a Secret from hand and trigger Phase Stalker in the same turn, play the Secret first so Phase Stalker pulls something else.
You have a couple substitution options. Wandering Monster is one of the worst cards in the deck. You can cut it for another Snipe and either an Explosive Shot, Rat Trap, second Pressure Plate, Snake Trap, or Flanking Strike.
Steamwheedle Sniper is bad. Don’t bother with it.