1) The night before set up fish to squeeze. It’s easier to inject more embryos when they are synchronized, and since you want to inject as early as possible, you can load the wells of the injection dish as they are swelling. They should all be injected before the first cell division to maximize the chance of integration into the genome (for stable transgenic lines).
2) Have two injection plates on hand. I prefer injection molds with the square-bottom wells. As the chorion swells the embryo gets wedged into the wells and won’t move. With the beveled-edge molds the embryos can move around as you try to inject, which slows down the process and also makes it a bit harder to get the needle to go into the chorion.
3) BAC DNA: I inject at 100 ng/μL. Higher than that gets really sticky and I’ve found that above or below that concentration decreases the number of positively labeled embryos on the following day. With BAC DNA just use a few μL. Throw out what you don’t use from that. The BAC DNA stock should be stored (long-term) in small aliquots (10μL) at -80°C. Once thawed, short-term it is good for about 6 months at 4°C. Do not re-freeze BAC DNA (it’s too big and degrades too easily in the process).