Preventing Interference when using RF transmitters and receivers
Those types of transmitters and receivers only work on a single channel. The receivers usually employ a form of active gain control (AGC), so will increase the gain until something (usually noise) is received. The gain is reduced to an appropriate level when a transmission starts.

Generally best practice is to:


Agree on a bit rate between the two systems (e.g. 4800bps). Generally
receiver/transmitter pairs will give you some guidance on these.
Transmit a preamble of 10101010 (generally somewhere between 8 and 40 bits) before starting the main transmission. This has two purposes - it allows the AGC to settle at
a good point, and can be detected by the microcontroller so it is
aware that a transmission is starting. 
Transmit a sync word e.g. 0xD5F7, and only listen to packets which have the correct sync word. The length of the sync word varies.
Use the rest of the data packet to detail the address, direction, and
data.


I have found that the VirtualWire library for the Arduino is actually a nice, clear example of how to go about this. Maybe take a look, even if you are working with another microcontroller family.

One further thing worth considering is the encoding of bits. You can just send a 1 as a 1 and a 0 as a 0. There are more complex schemes though. Manchester encoding ensures that each bit of data transmitted has at least one signal transition. This has two significant effects:


Regardless of the data sent, there will be an equal number of highs and lows sent. This means the AGC can work properly and there is no DC bias to the signal.
As there is a transition for each bit, it is easy to recover the clock from the signal even if it is not known. This really means you transmitters no longer have a need to use an external crystal - the internal oscillator is accurate enough.