The bonuses to the base abduction chance (which is 1%) comes from collecting space rocks, not keeping them on the lot or in the sim's inventory, and using the telescope. Using the telescope can be done anytime of the day, but it might be best to do it before the abduction time frame (midnight to 3 AM). These bonuses are temporary and only last through the next abduction period. If you don't get an abduction you need to repeat both (if you want the maximum chance) each day you want to try again.
Specifically, each space rock collected adds 15% to the base chance for an abduction up to 60% from space rocks. Using the telescope adds 14%. So the maximum chance you can get without mods is 75% that night. If there is no abduction the household must collect another 4 space rocks and use the telescope again on another day (again, to maximize the chances), probably before midnight but I'm not positive about that. I always collect the space rocks and use the telescope before midnight when I'm trying to get a sim abducted.
I have used the buydebug cheat to add space rock spawners on community lots so my sims would have plenty of space rocks to collect. That's something to consider if you are desperate. It doesn't matter who in the household collects the rocks or uses the telescope. Sometimes I have children do both (they, of course, do not get abducted).
Finally, the abduction chance is per household, not any individual sim. So, when an abduction happens, it will be random who is picked (assuming they are eligible for an abduction, i.e. not children, toddlers, etc.). For the other sims in the household, send them off the lot during the abduction time frame (midnight to 3 AM) leaving only the sim you want abducted on the home lot. But keep them off owned venues (the game can try to abduct sims from owned venues, but the abduction will fail and nothing will happen). I usually send the rest of the teens, YAs, adults, elders, plumbots, etc., in the household to the spa, or have them tour/visit various rabbit holes during that time. Mostly because in the one game where I had a male sim get abducted 19+ times (and had 19 alien kids, I was shooting for 26), that household owned most of the venues in town. Oh, abductions can occur on owned additional homes too, so don't send the rest of the household to one of those lots if they have any.
Leaving 5 or more space rocks on the lot adds to the chances of getting an alien visitation (where they show up and wander around the lot and scan things). Space rocks on the lot do not add to the abduction chances. As far as I know, space rocks in a sim's inventory don't do anything.
Lastly, the chance of a male sim getting impregnated is 33%. The sim must be human and male, occults cannot get alien pregnant. At least not without mods.
Speaking of mods, there are various mods out there that will increase the base abduction chance to 100%, increase the male pregnancy chance to 100%, and allow female sims to get alien pregnant. In the game I mentioned above I used NRaas Retuner to set the male pregnancy chance to 100% because I wanted to raise 26 aliens in that game (one for each letter of the alphabet). I haven't finished that game but I think I'm around Q or maybe T. Lol, it's been a while.
There are no cheats for alien abductions/pregnancy that I know of.
Good luck.