First you need to do The Island Note run so you are high level enough to tame one (lvl 65).

Then you need to find a good Crystal Wyvern.

The easiest Crystal Wyvern to tame is the Tropical because it is at a easy biome and very often to find.

If you found your Crystal Wyvern jump on his mount at the widest mount spot.

Now feed him Crystal.

Look how many Crystals you need to tame for the level.

Sometimes you fall off when your touching a mesh or when the Wyvern fly straight up or down so bring some parachutes.

Now you have got your own Crystal Wyvern :D.