To lockstitch by hand: sew a normal stitch (down, under, and bring it back up), then plunge needle in for the next stitch in the middle of the prior stitch and treat it as a normal stitch. Continue to do this. One step forward, one step back. This stitch holds amazingly well!

Tips and Tricks
pattern drafting and usage: measure twice, cut once. also, building up a repertoire of useful base patterns via store discount sales is priceless.
project planning: choose something that appeals to you, as well as your skill level. you should be able to fully visualize how you'll do each leg of the costume without major assistance from outsiders. if you don't think you can do it yourself, don't try it. keep in mind time constraints, too. for beginners and advanced sewers alike it is difficult to crank out a detailed costume in less than a month considering how hectic most peoples' lives are.
time saving: one surefire way to get things done is to create a takealong bag with current items that you're working on. once you've mastered the by-hand lockstitch, you can be more mobile.