Typically boot time is constrained by the speed of the HDD. You replace a HDD with a SSD and you'll see a significant improvement. This is also one of the few areas defragmenting can actually have an impact. You can limit the number of programs being loaded at startup, and even set some non-critical (but important) services to have a delayed start.
About the only thing you can do to speed up the process at the BIOS level is make sure the boot order is set to go to the HDD with the OS on it first, not check any other sources.