This advice is primarily aimed at the 2-player game.
First off, the importance of the bonus cards can hardly be overstated, especially the Rain cards. Therefore, for most of the game, the key to winning is to draw more bonus cards than your opponent. One of the best ways to achieve this is to make sure you get to place as many eruptions as possible. This means, paradoxically, getting your village to a HIGHER temperature than your opponent's, and making sure that it stays above until you cross into danger zone #3. This should be one of your highest priorities in the early part of the game. It is usually worth spending some cards for extra lava flow to speed this up, and spending some walls to impede your opponent's progress.
Ordinarily, save any rain cards you get until the end of the game. It is often worthwhile to convert some of your better cards into walls. The straw cards should usually be spent for lava.
Endgame: once someone has crossed into zone 3, the game changes drastically. Your goal now is to push your opponent to the maximum temperature as early as possible, while delaying this event for yourself. The bonus lava tiles from zone 3 are helpful for this. The ideal scenario is for you to enter zone 3 first, just barely, and immediately launch your opponent past you all the way to the end of the temperature track, while shoring up your own defenses.
Save your rain cards until you are forced to use them (at maximum temperature, or, preferably, in your last turn of the game). Depending on how many lava flows reach your village, you may want to put walls up for defense, but sometimes it is better to hoard them for the tiebreaker.
When playing with more players, a wider variety of scenarios are possible. Getting 3 rain cards should be much harder, and may not be enough to win. Pay attention to your opponents' strategies and respond accordingly.