Nowadays you can buy development tools that incorporate tons of form-behind widgets and code generation that can produce web pages with pop-out scroll overs, call-outs, and just about every kind of special effect imaginable. Is all of this necessary?
Unless you are building a data entry form (which has its own special challenges) you are probably better off just to make sure your web pages meet a certain set of minimum requirements. After you have thrown together your page, run it through a few simple tests:
1) Window Resizing
Open your page in a browser and resize the window to various heights and widths to see what happens. Did your layouts get mashed? Do you need to change column widths from fixed to a percentage?
2) W3C compatibility
Submit your page to the free W3C verifier, just as a courtesy check to assure that your tags are all balanced and that your links are all valid.
3) Powersave Mode
Fire up a browser on a smaller screen device and in the browser options turn off the setting that allows the web pages to "set their own colors." Also go into the properties tab on your desktop and change the color scheme to a power saving configurations, with a black background and white text. Now open up your web page to see what happened. Do you need to remove some "color" tags to keep it legible?
4) Just The Facts
Go back into the browser settings and turn off automatic image loading. Refresh your web page. Does it still make sense with just the facts? Did you provide the necessary alt tags so that the user can still figure out where to click for navigation?
Sure, spinning flashing widgets are fun to view on your site. For all of about ten seconds. What stays as important though is the actual informative content that you provide. Try to make it work under all conditions.