The game is derived from Quake III Arena. As such it is actually rather stable, as long as only default settings are being used. Settings are nativly stored in the game's folder. With newer variations it might also store those in the users home folder. So most problems can be remedied by starting fresh. This can mean, renaming the old configuration folder (backup). But for a more details description, why you might do, if the game causes you trouble, try one of the following steps:
Your CPU should not go under 75% to provide a smooth gaming experience.
In vanilla EF 0.28 to 1.2 and also older versions of ioEF, cMod and Lilium Voyager there is a bug that may prevent you from playing against bots when opening a listen server. It might even block you from putting one up in the first place: When setting g_password and adding bots later on, they can “connect” to the server but not enter the match. If you set g_password in hmconfig.cfg and make it read-only, the game will set g_password accordingly, which will also prevent yourself from joining the match. So if you want to play with bots, don't use it.
Especially with the GOG version you might notice that your shadow seems to be translucent or glitching somehow. This is due to not properly working volumetric shadows. Those were supposed to look better than the spherically shaped shadows, but never really worked on the original game. (This goes not for the ioQuake based versions.) In order to get rid of this problem, set cg_shadows to 1, instead of 2. The shadows might look more dull this way, but they work.
It is known to happen on MacOS, that the game does not find the actually already inserted CD, when trying to play it. This can be solved by replacing the »Bink Carbon Library« in the Elite Force Folder with a newer version. You can get it from the Neverwinter Nights. The version 1.6a coming with »Railroad Tycoon 3« or »Call of Duty Unite Offense« single player does not work however.
It might be necessary to set r_smp to 0. This turns of multi CPU usage.