Whenever cards are played, put them into the appropriate play area starting from left to right in the order in which they were played. When resolving the order of START PHASE or END PHASE effects (or non-Hero effects with a unique icon, like Omnitron’s Exterminate and Fabricate text), resolve them in the order those cards were played, from left to right in your play area. During Hero turns, before the start of any phase, players may reorder any non-character cards in their play area before resolving them from left to right.
In ambiguous situations, such as tied HP or multiple targets being damaged simultaneously, the players choose the outcome or order of effects.
If there’s ever any confusion about how a particular card works, try reading it out loud. Often, parsing a card’s text out loud can help explain the intent of the card.