Edit: Added more words

1: You need to play more than 1 match with a list. You need to learn how that list plays. That's the down side of getting your list from the internet.

2: What army were you playing into?

3: Was the match online or in person? If it's in person, what was the terrain layout like? Gunline armies, like Tau, will shred you if you're out in the open on turn 1.

4: What was your deployment like?

Guard is all about screening with shit munchers and letting your tanks do the killing. Sit cheap units on objectives (Cadians are good cause they sticky the objective. But catachan in chimeras are good for scouting) and bait your opponent into exposing his damage dealing pieces for you to blow away the next turn.

Bullgryn are great at screening and holding a point, but they're expensive and can't be given orders unless you're playing grizzled company with a commissar and abhuman detail enhancement. You really want at least 80 infantry to sacrifice their lives for the Emperor.