[Legolas]

You can use and write a variety of scripts but the standard script set is the one used by the official campaign's plot NPCs.
In the toolset, on the standard creature palette, go to NPC -> Other. Choose Edit Copy for any one of the creatures listed there (apart from Volkarion), and select the Scripts tag.
If you assign the scripts you find there (nw_ch_ac series) to your NPC they should act just like an OC henchman.

Of course, these aren't the ultimate in henchmen scripts. You can find others in use in the SoU and HotU modules which offer more functionality (like the x0_ch_hen_ series), and there will be henchman script sets on nwvault as well. But the OC scripts cover the basics and so they're a good place to start.