Prepare the soil and fertilize as you would in the spring. See http://www.bookstore.ksre.ksu.edu/pubs/mf319.pdf for more detail on asparagus and http://www.bookstore.ksre.ksu.edu/pubs/ep99.pdf for more information on rhubarb.
Water well after planting to ensure good root/soil contact. Mulching would be helpful on the rhubarb to prevent the plant from heaving out of the soil during the winter but asparagus requires no such treatment as it is planted much deeper. (Ward Upham)