Singletracks makes a good point below, don’t ride a road bike that’s too aggressive with the riding position, more upright seating is better to get used to it. You can always adjust later as you get more comfortable. And either use your mountain bike clips as you’re used to them already as Singletrack suggests, or do what i did and just ride with toe straps till you get comfortable on the road bike. Then switch to clips.

Other than that, I can’t really say due to my lack of experience as a road biker. Maybe others can chime in?

From there, start by clipping in whatever foot is downhill. If the drop off on the trail is to the left, clip in your left foot–do not clip in your right foot first. If you cannot clip in first with your left foot, practice clipping in and out with both feet at home in a grassy yard or field. Use your uphill foot to steady yourself on the uphill side of the trail. Push down from the top of your pedal stroke with your downhill foot, and as the other pedal comes around, get your uphill foot on it and apply smooth, even pressure. It is important, and more important the steeper the hill is, to get immediate power as the other pedal comes around (not alot, just enough). Don’t worry about clipping in your second foot yet (unless you’re very confident)–just worry about getting power going. Once you’re under way, you can make sure you’re clipped in to your satisfaction.

If the trail is very steep, you can start with your bike sort of angled across the hill, with your back wheel off the trail a bit and your front wheel on the trail to lessen the initial angle as you begin. This technique is kind of difficult to explain without showing… maybe a topic for a video blog? But for about 90% of my remounts, the above paragraph works great.

Finally, if you live in a place with a lot of trees, you can always grab a handy tree, hop on the bike, steady yourself, clip in, and start again. That makes it dead easy