Categorize by screen
Try considering the way you use your device. Widgets and shortcuts that you would be using at the same time might as well be in the same area. This is especially important when you're relying on glanceable information. You can think about your phone as a heads up display. You go to a particular screen, and you get information pertaining to a particular specialty. For example, you might choose to keep social networking widgets together so you can check in quickly, and keep them out of the way when you have other things to do.
Some functions might not need a whole home screen panel. In those cases it's fine to sub divide the screens. If you know that productivity content on the bottom half of screen three, that's just as useful as devoting a whole screen to it. Well, provided the top of screen three isn't filled with games. Then that to-do list might not get done. It's a good idea to keep entertainment and social networking content away from things you might need at work.
In general, keep the things you use frequently on the main home screen panel. That way you can access them after a home button press. Apps like Gmail, Maps, and Voice are some that I keep on that screen. This is also a place to keep a clock and weather information if you like. Beautiful Widgets has been in this space for as long as I can remember.
Make system tools more accessible
The battery meter on Android is notoriously inaccurate. It seems to have too few steps to offer a real indication of charge. If you're worried about battery life, just use one of the many available widgets to keep an eye on the charge. I'm fond of placing it front and center on the main home screen. Pressing the home button will offer a quick reminder of better level, and that can be very useful. Similarly, there are widgets for showing more accurate signal indicators. This can be helpful when you're having issues with service. Those bars in the status bar can't necessarily be trusted, so real dBm numbers can be of use.
Going back to the point from above, you should keep these system tools and statistics together if possible. If you need to use one of them, the other might be of use too. You don't need to dig through Android's menu system to find out how much storage space you have, or what your real battery level is. It can all be there on the home screen.
It's also useful to make space for a folder where you can keep settings shortcuts. There are times when you need to access a menu in the settings, but actually getting there can be a pain. Using AnyCut, you can make a shortcut to any location in the menu. I have a folder of settings with links to phone status, batter use, Wi-Fi settings, Manage Applications, and the Testing menu. This is a big time saver and a great addition to any home screen.
PerformanceYou need to be aware of the performance hit filling up your home screen with widgets can cause. This might be a mild difference, but you should be cautious you aren't actually hurting your experience while trying to help it. Watch for laggy scrolling, or slow orientation changes when you open a keyboard (if you have one). This is less of a problem with newer devices, though. You should check a problem app's settings to see if you can improve performance.
For instance, I use a calendar widget called Pure Calendar. I noticed it was slow to refresh when I rotated the screen. It turns out there is an option to disable redraw and improve performance when changing screen orientation. Now it pops up faster, and there's no real negative I can see.
Replace Android default widgetsIt's good of Google to offer so many widgets with Android, but if you want the perfect home screen interface, it's worth shopping around. That's one of the strengths of the platform. If you don't like how something works, you can usually replace it.
The power control widget is an excellent addition to the OS, but it is a little limited. Some third party options offer more controls in the same space. Just paging through the Market offers multiple options that can make your home power screen widget more useful. As mentioned above, Pure Calendar Widget is a great alternative to the Android calendar widget, but there are many alternatives. I also like to use a third party music widget, as the stock one is a little dull. Sense has a more attractive widget, though.
One of the benefits you see from using third-party widget solutions is that they tend to fit into more home screen layouts because they offer more sizing options. You might have a little extra space, and a bigger calendar widget would be useful. Or maybe you only need a few power controls, and space is at a premium. In either case, you can make it happen with third-party widgets.