Tips and cases to avoid when singals acts like antenna
Frequency has a wavelength. Higher frequencies physically take up "less space" as they vibrate. As the length of an (unshielded) conductor starts to approach and exceed one tenth of the wavelength, it starts to behave like an antenna. So if you don't want the trace to start picking up any EMI (become an antenna), keep it's total exposed length to less than a tenth of the wavelength. Often, 1/4 wavelength is heard in discussion. This is another important one, as traces will definitely behave like antennas at this length. (Research 1/4-wave antennas for more information.) So that is the length to avoid.

For example, the wavelength of 2.4GHz is about 5 inches or 12.5cm. One tenth of that is about half an inch or 1.25cm. Exposed traces longer than this will start to pickup EMI. And a specially-designed trace, exactly 1/4 wavelength (0.984 inches, 2.5cm), can work very efficiently as an antenna itself.

Receiving signals is less critical of PCB design than sending signals. This is because the intensity of the generated EM field decreases at the square of distance. A radio station may transmit 5000 watts of power, but that signal is incredibly weak when it reaches a radio (5uW.) Therefore, less shielding would be required in a receiver circuit, than the radio transmitter. Near the antenna of a transmitter, the signal strengths are orders of magnitude greater, and a faulty-designed trace can couple this signal (EMI) as dozens or even hundreds of volts, and cause erratic behavior.

If you have a 4-layer board, just dedicate the side with the antenna on it as a ground plane, and don't put any traces on it at all. That will provide total shielding (assuming the signal doesn't reflect around the room onto the other side of the PCB.) Small components (less than 1/10th wavelength in size) can be placed on this side, but I'd keep them as far away from the antenna as possible. Larger components or exposed leads/traces longer than 1/10th wavelength may require external shielding. If this is not possible, or the antenna is on the edge of the PCB (radiating onto both sides), then both sides will have to be ground planes.

For 2.4GHz, this can be quite tricky, as the dimensions are quite small. For lower frequencies such as radio however, the wavelengths are much longer, so design limitations are much more relaxed.