On a VERY basic level, my RFTG choices work like this:
Pick Develop if you want to build a development
Pick Settle if you want to settle a world
Pick Trade if you want to trade
Pick 2x VPs if you want to get extra VPs from your consumption of goods
Pick Produce if you want to produce goods
Pick Explore if you want to ?????????
Where do the 2 Explore cards come in? I guess the obvious choice is "If you need more cards and have no better way of getting them." I've gone through a few games without ever picking explore because it essentially gives you a 1 card advantage if you pick the 'look at 1 more, keep 1 more' card and an advantage of maybe getting a slightly better card than your opponents with the 'look at 5 more cards' card. Both Develop and Settle give you a 1 card advantage at the very least, both Consume phases can lead to big card advantages, and Produce can set you up for an amazing next turn and sometimes give you card advantage in itself.
Is my analysis roughly correct? With all these things going against it, when should I pick each different Explore card in my phase selection? It seems to be a desperate pick when you have virtually no other options, so at the very least you can be happy with getting a net advantage of 1 card over all of your opponents, or are hoping for a certain card, have a lot of cards in you hand already, and have no better options.