Being a single lass, almost any time a bike needs to go into the truck (Tacoma), I'm doing it by myself. My ramp is skinny (wide enough for the wheels, naturally, but not for me to walk up next to the bike - have to step into the bed) and about 6 feet long.
I just put a bungee from the hinge of my ramp to the truck's hitch to hold it in place. I've never had a problem with it slipping.
Biggest tip would be to minimize the incline on the ramp, if at all possible. Since there's no way I could physically push the bike into the truck, I end up putting the bike into gear and getting the bike into the truck under its own power. (I walk alongside it; too much of a sissy to try riding it in.) But, the greater the incline to get into the truck, the greater your speed needs to be to get up it... which means a greater chance of mishap.
2nd tip - if the bike stops or stalls on the ramp, don't try to power it up. Just roll it back and start over again.
Not sure what else to share. It's definitely a harrowing experience the first few times, but once you get the hang of it, it isn't too bad.