1. Make sure their first couple of days are laid out but give them downtime where they can just poke around and read some material, don't fill the first few days with person after person. Fine to do that a little but provide an outlet for them to do some discovery too.
2. Have as much of their work area ready as possible. If you are letting them order their own equipment that's cool, but hopefully you did that so it was sitting ready for them on day 1. If not you are wasting both your time, but I know it is hard sometimes too.
3. Assign them a few tasks within the first day or two. Make them debugging or documentation tasks or a combination of both. I like to take low hanging fruit problems when we have them that just keep getting skipped over and hand those to new people to get acquainted. Documenting that library or component you had to crank out last year quickly but never got back to is also a good thing.
4. Ask each of them to keep a journal of things that they felt could be better. After a few months sit with them and understand the suggestions and implement solutions where you find patterns that are more than a personal preference type situation.
*edit: a few words