I think the first question you should ask yourself is how often do you plan on using your tent and will you be sleeping on air mattresses or does a camping mat work for you? If you plan on camping quite often, in many different types of conditions, or if you want an easy to travel with tent, I would highly recommend spending a little more and buying a tent by an outdoor company like marmot, big agnes, sierra designs etc. I definitely agree with a previous poster that you should put something under your tent. We camped for years at the fort when i was younger and rain does gather in the shell mix and form lakes, plus it also does stick to the bottom. I would also recommend that you make sure that your tent is standing higher than surrounding areas and dig drainage moats if it rains and you find it gathers. We had to do this for my sister one year and she felt like she was living in a castle. Otherwise it is just fine. We used a large eureka tent which in our family was called the hilton, because it was great. I have bought a more expensive tent for my family by sierra designs, which has a full fly and weighs very little despite its size, which makes it easy to fly with. The full fly allows for shoe storage and other things under the fly by the door as well as being able to open and close the tent with the doors covered as well as open windows which are covered, which is great for rain and heavy winds. I think it also keeps us warmer at night, but the mesh top of our tent under the fly allows for awesome ventilation, a plus when it is humid.
Excellent advice.
--However if you are couples or a mixed party (2 guys, 2 gals; family with teen girl/boy mix) I would suggest getting two tents of quality (the brands listed above are especially recommended);
-- Remember the 2 person tent is for two people sleeping taking up the entire floor of the tent, if you want room for 2 and gear start with a 4 person
--I can vouch for Marmot (spec. Limestone 6) as an excellent brand,especially in heavy/torrential wind and rain.
-- Another recommendation is get a tent you can stand up in (my wife's requirement), it makes quite a difference in dressing and comfort
--remember you get what you pay for, the difference in cost is typically not the size but in the ability to set up the tent quickly and with fewer people (really important in a downpour), and quality of poles, rainfly,zippers, ventilation, and interior storage.
-- If the tent does not come with ground sheet buy one (preferably from the tent manufacturer). This will not only protect the tent, but allow you to store the wet, dirty ground sheet in a plastic bag separate from the tent when packing up. ( I always have at least 2 13 gallon garbage bags when camping, one for wet rainfly and one for the groundsheet: just make sure to take out and air out as soon as you get home)
Also cots are a sure fired way of getting a good nights sleep with no chance of deflating.
There is always more as scouts say, but that should give you some things to think about.