These are not my creation, but I've found the tips in this webpage very useful for mastering iPad (and iPhone) typing. Full credit goes to that site.
There is a list of ten useful tips for making efficient use of the onscreen keyboard(s) in iOS based devices. Some of them are generally known, such as the URL autocomplete and spellchecking completion, but others are less widely publicized, such as the final tip about toggling the alpha and numeric keyboards.
[crarko adds: I tested some of these on my iPhone, and they worked as described. There are some screen captures and a video on the referenced web site which shows how these tips appear. I'm putting this up because keyboard shortcut hints are generally useful things, but I refer you directly to the original site to preserve their copyright.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100610143124863