Pre-flight checks are essential for any flying model airplane. Even obvious things can be missed if you're too eager to get the plane in the air, and such mistakes can often result in a crash.
Your airplane's instruction manual should outline the pre-flight checks needed for that specific airplane, but as a general guideline basic checks include:
Wing and tail securely fastened
Prop (and spinner) secure
Control surfaces moving freely and correctly
Motor operation correct
Everything inside is secure (no loose components, especially battery pack)
All servo horns and linkages secure
Radio control transmitter batteries OK
This last one, the range check is absolutely crucial and mustn't be forgotten! The purpose of the range check is to make sure the radio signal from Tx to Rx is strong, so that you can fly your plane at a normal distance away from you without it going out of radio range.
To perform a range check with a MHz radio, switch on the transmitter and then the receiver, and collapse the antenna (i.e. put it fully down). With a 2.4GHz radio you will need to follow the manufacturers instructions for getting the Tx in to range check mode.
With your Tx prepared, walk backwards away from the airplane for 30 paces or so. As you walk away from the plane, keep moving the control surface sticks of the Tx (but not the motor stick!) and closely watch the respective control surfaces of the airplane.
If you only get a few paces away and the surfaces start 'twitching' or not responding properly to the stick movements, do not fly. Check the transmitter batteries, they may need replacing/recharging; low batteries in the rc gear drastically reduce the radio range. Also check for loose connections to the receiver etc.
If the batteries and connections are OK but the control surfaces still don't respond properly then other people may be flying model airplanes nearby on your frequency. Again, do not fly if this is the case. Interference is a big killer of rc airplanes and you need to be sure that your frequency is clear before you get airborne.
Whatever the reason, do not fly your rc airplane if you see that control surface response becomes unreliable before you reach 30 paces or so away from the plane. Identify and rectify the problem before flying.