I agree with what Raphael says pretty much. On the topic of Sparks, I'll give the opposite advice of "don't play too cautiously". If they start with a Spark, go ahead and summon that Fire Snake turn 1. There's a 50% chance that the Spark will be alone, and that's a quick +1 card advantage for you. If your opponent does have a second Spark, your Fire Snake absorbs 2 damage for you, which you'll need because your opponent will follow the Sparks with a Gargoyle and then a Bloodlust. In the rare case that he has three Sparks by turn two, well, you're screwed anyway (unless you're Banebow), so it does not matter.

Basically, assume they only have one Spark unless you see two.