I usually get CEV if I am reasonably high and haven't been on a smoking binge recently. The effects are boosted if I've had any stronger things within the last few days, depending on how visual said stronger things are. Don't expect anything incredible, it's mostly 2-d colors moving and dancing (for me often lots of larger and smaller circles, thousands... they can make patterns but usually not unless I'm fucked enough that modest visuals are not the center of my attention.
). I can't be sure I consistently got CEV before ever doing any psychedelic drugs.
Tips if you want to try to get CEV (definitely don't need all but some help):
1. Have tripped recently
2. Don't have smoked recently
3. Be well rested
4. Get really high! Pure sativa seems preferable
5. Be in a dark place. Ideally sensory deprivation. Also try a single light source, not too bright in a dark area (i.e. computer screen)
6. Use music to boost your fucked-up-ness, and get as into it as possible. For me the peaks of jam music, where there is the most "it," are ideal.
7. Don't try to get visuals, relax into being really gone and then notice if anything is going on visually.
8. Keep your eyes closed... it takes several seconds if not more for CEV intensity to ramp up.
9. Pixelation is often a precursor to CEV
10. When in doubt try rubbing your eyes to get a phosphene show (does some cool stuff when you are sober too, esp. in the dark). Just don't overdo it!
Good luck... keep in mind that not getting CEV has its benefits as well. If I am tired, sober and have smoked in the last couple of days I get mild OEV pixellation on white surfaces, which can get distracting.