I could write about invis for ages but I'll try to be concise.
- Invis is not the all powerful zerg enabler it appears to be, without a modicum of practice and, then, skill.
- Mr. Cow is pretty well practiced and therefore skilful. You will be able to do it as well as him but it takes time.
- Invis gives invis, if they don't have True Seeing, but still triggers Listen checks, which can get you aggro.
- Some mobs, like Spiders, have tremorsense and will always aggro a non-sneaked runner, invised or not.
- You can skirt round mobs to lessen the chance of drawing aggro or triggering a Listen check. The bigger the space between you and the mob, the better. Get too close and they will see you clearly, invised or not. There are two radii I see around a mob; 1) auto-fail, 2) trigger listen, then outside of that I know I'm ok. You'll get to learn them and visualise them too.
- A good Jump skill score helps a lot to navigate crowds.
- If you do fail Listen checks and get some follow you, resist temptation to engage and stay invised, given enough time and distance the aggro will drop and DAs reduce back down.
- If you do fail Listen checks and get some follow you, sometimes this can trigger aggro on other mobs. It might be better to take a slight detour. (I'm not quite sure still what the criteria around this is, Cow may know!)
- When you have to pull levers, try to both pull mobs away with Listen check fails first and also re-invis immediately after you pull. Start your invis clickie/pot/scroll applying about 15-20% before the end of the lever timer bar. You'll still get the pull and you'll be visible for less time.
- When you open doors, do the above as for levers. Also move off to the side and then use the door, so the mobs the other side don't all see you.
- Mobs seem to be more forgiving the first time you invis past them. If you're in a group, even duoed, the second time seems much more likely to draw a Listen check fail and aggro.
- Haste pots are better than Haste clickies, which seem to trigger multiple Listen checks in a radius around you.
- Some other spells seem to trigger Listen checks, even on clickies, figure them out and either pot them or avoid them.
- Hesitation is bad. Once you know the quest, run run run and don't look back. If you get red DA and die, swallow it and try again.
There's almost certainly more but I forget some and I want to get in the game this evening. Hope it helps. Some of these may be based in superstition/cognitive bias. If so, I'm sure someone with better game rule knowledge will be along to correct me soon. Regardless, I work to these rules and do ok.