Your best bet is to Google Sedona Photo opportunities to get exact direction, but I can tell you that Coffee Pot Rock is popular as well as the Church in the Rocks. Some of the best lookout spots, like a spot off Schnebly Hill Road are on the west side of Sedona, so you want to be up there in the morning for the best light to photo the city, and of course in the evening for those sunset shots. Coffee Pot Rock (if memory serves) is best shot in the AM as well. The church/cathedral in the rocks faces south by southwest (again, if memory serves) so you can shoot that midday or after noon if need be. Remeber to pack a polorizing filter so that blue sky will pop and make that cathedral stand out even more. Asside from that, once the sun starts going down - you just want to shoot everything in Sedona. If you're serious about getting some good shots, you may need a couple days there so you can shoot and scout the first day, and get what you missed the second.
Depending on when you go in May, the wildflower season may be dwindling down in the Valley (Phoenix), but parts of northern AZ may be ripe for those types of photos. Bring the widest lens you have, a polorizing filter, a tripod and a remote if you have it, and have fun. Oh, and there are plenty of close-in photo ops just walking around Sedona too.
