Small Swipes for Large Actions -- No doubt the iPad's biggest selling point is its large screen, especially compared to an iPhone or iPod touch. But it can also feel like a liability at times.
Add Up to Six Apps to the Dock -- The iPad ships with a basic iPhone layout, which includes four apps on the Dock that appears at the bottom of all Home screens. Take advantage of the extra screen size and add up to two more. Tap and hold an app you want to add until all of the apps begin jiggling. Then drag the app to the Dock. Press the Home button when you're done.
Jump to the Top -- This behavior was introduced on the iPhone, but you need it more on the iPad's large screen. Tap the status bar at the top of the screen to jump back to the top of the page or window you're viewing.
Lock That Rotate -- This may not qualify as much of a secret, since Apple promotes the feature, but in my early experience, it's terrifically useful. Flick the switch above the volume controls to lock screen rotation. The iPad is quite sensitive to orientation, and rotates its screen with little provocation. Locking rotation means sticking with the view you're in, even as you shift position, or place the iPad flat on a surface.
Quick Mute -- With that switch repurposed for rotation lock, what happened to the iPhone's capability of using it to mute the volume? On the iPad, press and hold the volume down button. After about two bars of volume, the iPad's volume jumps to zero. (Take Control author Sharon Zardetto gets credit for pointing out this tip.)
Use Spotlight to Launch Apps -- Again, this is something not unique to the iPad, but I never used it on the iPhone. Once you've accumulated a bunch of apps, it can take a while to flip through several home screens to find the one you want. Although there's no equivalent to LaunchBar for the iPad (believe me, I'd buy it in a heartbeat), here's the next best thing.
Type an Apostrophe from the Basic Keyboard Layout -- The iPad's onscreen keyboard approaches the dimensions of a full-size keyboard (in wide orientation, at least), but accommodations still had to be made to get it to fit. One of the most maddening is the lack of an apostrophe key. I keep hitting the Return key with my right pinkie finger when I mean to type an apostrophe. You need to tap the ".?123" button to reveal the correct key, which itself is in an odd position at the bottom of the layout.
Type Curly Quotes -- Similarly, tap and hold the single or double-quote key to get a selection of real quotes (the curly kind) as used in major languages that use the Roman alphabet. This feature is in the iPhone, too, and I'd never discovered it, probably because I didn't notice typography as much on the small screen. When putting together a Keynote presentation, however, those curly quotes make a big difference. (Straight quotes - disparagingly referred to by typographers as "typewriter quotes" - often indicate the person is a graphics amateur.)
Access Alternate Characters -- This tip isn't specific to the iPad, but it's worth remembering. Touch and hold a character on the onscreen keyboard to view related characters. For example, holding the E key brings up accented E characters, or holding the $ key brings up other currency symbols. (Thanks to reader "Arthur" for the reminder.)
Better Word Suggestions -- This one isn't so much a tip as it is an observation. I've noticed that the iPad's word assistance is better than the iPhone's. When I miss the space bar while typing (especially now as I'm just getting accustomed to the onscreen keyboard), the iPad automatically suggests that something like "feellike" should be "feel like".
Practice Good Typing Form -- I never realized that I rest my hands on the keyboard when I type until I started using the onscreen keyboard where every contact on the screen creates an action. Keep those fingers and palms up as you type.
Zoom Way, Way In -- The Zoom accessibility option that's in the iPhone OS is even more helpful on the iPad than on a smaller device because of the additional screen territory. You can turn this on from Settings > Accessibility > Zoom by flipping Zoom to On.
Use an External Keyboard -- When you want to do some extended typing, pair the iPad with a Bluetooth keyboard or plug it into Apple's iPad Keyboard Dock. In addition to better ergonomics, this setup gives you access to common keyboard commands like Copy (Command-C) and Paste (Command-V), and lets you make selections of text by holding down a Shift key and using the arrows for navigation. You can also delete words with Option-Delete, and entire lines with Command-Delete.
Manage a Bluetooth Keyboard -- If you've paired a Bluetooth keyboard, be sure to turn it off or disable Bluetooth when you're not using it. If you enter any editable text field that requires text input and the keyboard is within range, the onscreen keyboard won't appear.
Master Shifting -- The iPad has territory enough to offer a Shift key on both the left and right sides of the keyboard and for your hands to lie flat on the screen. This lets you take advantage of a feature found in the iPhone OS, but not quite practical to use on the iPad's smaller siblings: you can hold down the Shift key while typing a letter to a get a single capital letter, then release, as with normal physical keyboard touch typing. This can dramatically increase your typing speed. You can still tap a Shift key, which turns blue, and then tap a letter to get a single capital letter.
Easier Text Selection -- This feature is also not unique to the iPad, but it's worthwhile and something I never knew about until a few days ago. Double-tap and hold a word to select it to circumvent the need to tap the Select button that appears, and then drag to extend the selection to additional words. It works on both sides of the selected word; when you're moving just the selection handles, that's not the case.
Replace Text -- When you select a word, the familiar pop-up options appear: Cut, Copy, and Paste. The iPad adds a new option: Replace. Tap it to view alternate spellings or corrections.
Use the Spell Checker -- The iPad includes a built-in spell check feature that acts the same as the one in Mac OS X. If you misspell a word, it appears with a dotted red underline. Tap the word to view suggested spellings. (Thanks to reader "Rivka" for pointing this out.)
Watch iTunes-Purchased Movies on an HDTV -- Movies in the iTunes Store are wrapped in Apple's FairPlay DRM, which uses HDCP to ensure that only devices that support HDCP can play the video. If you bought the iPad Dock Connector to VGA Adapter and hope to play video on your recent HDTV, you're out of luck because it won't carry the digital signal. If your television has component connections (red, green, and blue cables), buy Apple's Component AV Cable kit and hook your iPad to the TV. Voilà! It's like having a portable Apple TV with you at all times.
Always Show Bookmarks Bar in Safari -- I use MobileMe to sync my Safari bookmarks to the iPad, and keep my most-used bookmarks handy by storing them in the Bookmarks Bar on my MacBook Pro. Safari on the iPad also features a Bookmarks Bar, but it's hidden by default. In fact, the only way to make it appear is to tap the Address field to position the cursor there. Instead, go to Settings > Safari and turn on the Always Show Bookmarks Bar setting to make the bar appear at all times.
Two-Finger Zoom for Web Video -- Reader "Joe" pointed out that when you encounter a video on a Web page that the iPad can play, touching it with two fingers and expanding (the opposite of the pinch gesture) zooms the video to full-screen mode.
iBooks Easter Egg -- I haven't heard of any Easter eggs - hidden programming surprises that developers sometimes include in software - in the iPad's software, but I did discover something similar. In the iBooks app, touch and hold the shelves that display your library, then drag down as far as you can to reveal a little surprise hidden behind the faux wood.