Biofilm is the most important which means LOTS of surface area that also doubles as hiding places. IAL leaves are good because the babies get on the bottom side of the leaves to eat and molt in peace. SPonge filters or pre sponges, moss balls, and wads of moss are good. Adding airstones is recommended, avoiding temperature changes of more than 3 degrees during water changes along with avoiding sudden shifts in parameters will also help.
Keep in mind some shrimp just have a certain mortality/survival rate that you are working with. With CRS/CBS I've heard 80-90% survival rate is normal if parameters are ideal. Now, if the babies are born in too high pH they can die. I had a batch of A grades born in a tank of 7.4-7.6 pH. The adults lived fine. The babies never made it past day 10. In another tank with more ideal params I was doing well to see 65-70% survival rate but still, better than 0%
. I don't take survival counts until 10 days-2 weeks on bee shrimp (CBS/CRS/Goldens). For something more difficult like OEBT you don't even bother counting until they are 3 weeks old at least. Neos typically have higher survival rates overall. I have tibees that I had 95-98% survival rate on 3 different batches. So, the point is it varies a lot by species plus the other factors like diet, biofilm, temp, params, etc.