Since I have had numorous of problems with my ESP8266 modules, this is what I generally watch for:
Output is 3.3v
Swap over tx and rx. Some boards have them swapped for some reason (searched for days for this!!)
When uploading the code, first the code compiles, then the code uploads. During the compile process, keep the reset button (or pin) pressed. As soon as you see the "uploading" status message, you can release it.
Make sure the GPIO0 is connected to the ground and (depending on which version you have) the GPIO15 as well.
When grounding the GPIO0 and GPIO15, use a resistor for each (between 2K and 10K will do).