I used a plank as a ramp. Or back the car up to a slope like the earth banks found alongside Dartmoor lanes. A second pair of hands helps but it can be awkward with only one person. It doesn't always go smoothly as you can see from this video at 48.23.
As Doug says one wheel at a time. The front is lighter and once the front wheel is in it holds the bike steady so the rear wheel can be lifted in.
