Santa Elena, a city of 25,000ish people is located on the south edge of Lago De Peten Itza and is joined to Flores by a causeway. It's not a great city but if you are staying in Flores, this is where you can get stuff done. Since Flores doesn't have a bank, you come here to grab some cash. Flores' businesses are more orientated towards tourists so if you need untourist things, this is the place to come to. The flores airport is actually located here. Santa Elena also has a selection of hotels and restaurants but I didn't go to any of them cause I quite enjoyed Flores and spent most of my time in the area, there.
Tikal is the number 1 site in El Peten and probably all of Guatemala (the other place that give it a run for it's money is Antigua). I didn't take full advantage of Tikal and actually kinda forced myself to come here. I went here the day after finishing the El Mirador trek (around 130 km in 5 days). Tikal is an amazing site and simply you just have to go if you are in the area. There are just so many large structures and most of them you can climb. It's spread out over a fair size area although the tourist areas are fairly compact, still expect to do some walking.
This UNESCO World Heritage Site may have supported a population up to 200,000 people. It was the largest Maya city of the Classic Era. It was often at war with other Maya cities at was eventually defeated by Caracol who replaced it as the top dog of the southern Maya Lowlands.
Entrance to the park is Q150 and the general gates are opened from 6 to 6. There are lots of buses going to and from the park. It's very easy to arrange your trip to Tikal from many of the local towns as this is main reason tourists come here. There are few hotels right next to the park if you want to take full advantage of Tikal as well as restaurants, a museum and souvenir stores. I had no problems with security here, there were problems here and the beginning of this millenium, but with the tourist police, that has mostly disappeared now.
If you are a Star Wars fan, Tikal was the site of Yavin 4 in Episode 4: A New Hope.
Flores is the capital city of Peten and is located on an island in Lago Peten Itza with a population less than 14,000. The main reason people come here is to use it as a base to get to Tikal which is not to far from here. I quite enjoyed this town even though it is obvious that it is mostly designed for tourists. It is a pleasant town to walk around with it's red roofed colonial buildings and cobble stone streets. There are a bunch of hotels, restaurants and travel agencies that you should have no problem getting any of those. There is no bank here and you have to go to Santa Elena across the causeway if you need to grab cash. Flores is a clean and safe town and almost doesn't seem Guatemalan (apart from Antigua).
This place also has history. In Pre-Columbian times, it was known as Tayasal. It was also the last place the last Mayan civilization held out against the Spanish conquers.