A few things...
Remember to always use the correct DOCTYPE declaration. This is the best way to make sure the browser uses the right DTD and processes code the W3C way, not according to the browser's standards.
I always consider the points in the W3C Web Accessibility Initiative (although I don't try to conform to it; it's crazy-strict) when making a web page. WAI sets certain goals to make web pages as accessible as possible to all browsers, people on any computer with any internet connection, and people with disabilities. This includes designing web pages so that they don't need stylesheets to be properly viewed. Information on WAI can be found at
http://www.w3.org/WAI .
Flash...
I prefer not to use flash. Not everyone has flash, and loading time can be very long. Visiting flash sites is not worth it to me: I use a slow Mac OS 9.1 with 56k dialup. As said above, flash files are bandwidth eaters, and it doesn't always look good.
Frames... Use of frames in general is not recommended. Not all browsers support frames. Frames can make it hard to navigate a web page if a frame is too small.
<noscript> can be used to deal with browsers that don't support script, but that can be unreliable. Once in a while there are also differences in the way browsers handle javascript. Better to have the server handle script (i.e. with php) where the output is going to be consistent than to have the user's computer handle script.
Dimensioning and resolution: If absolute units must be used, then px and em should be used. pt for font-size is not consistent.
Using percentages can be tricky. Just make sure that all related or nested elements agree with each other in terms of size. Dealing with resolution problems doesn't have an easy solution.