For making calls and sending texts and stuff:
Avoid covering the bottom of the phone because that is where the antenna is (I know...stupid place). If you remove your SIM card/Micro SD cover, you'll see a little brass colored strip on the side. thats the antenna. Make sure its shiny. After about 2 years it will start discoloring.
If you can, use speakerphone and hold the phone so the bottom is somewhat facing up.
When sending texts, hold the phone so the bottoms up then press the send button. This will help make sure the phone retains connection throughout the sending process and doesnt stop halfway, at which point youll get a message sending failed message.
If your in an area where your pretty sure there should be more signal (you see everyone else using their phone), and you dont have signal, you may have a defective device. I've been under 4 feet of concrete and still had 2 bars with my hand covering the bottom. My DeLorme PN-40 GPS didnt have signal, and its one of the best GPS recievers out there. goes to say how good the inspires antenna should be...