Just my two cents:
Personally, I would make the layout fluid, so that it auto adjusts itself according to the length and breadth of the display.
Remember many phones have accelerometers which can change the direction of the page, when tiled sideways. In this case, horizontal scrolling is a big no-no.
Just keep all useless things aside and present only the basic information, advanced or details information should be places under More button.
Don't use Images, or I say - Use it as minimum as possible. This would take the most of the user's bandwidth. If you are targeting this for people under GPRS/EDGE , then better avoid Images even more. People on 3G have a better chance.
You can have a look at Facebook or Gmail mobile interface to have an idea. Google Reader's mobile interface is also good, but still not upto the mark.
I don't know how much people would agree with me - Keep AJAX low. Most phones can't handle so much load if your page is highly ajaxified. Remember, it is a mobile and not a computer. It does have some limitation. Probably very high end phones can render it, but to keep your userbase strong, minimise the use.
Content Load: If the page takes just to much time to load, then probably the user won't bother using it. They would prefer to use any other alternative/service which can get his/her work accomplished.
CSS: Make less use of CSS as much as possible. Use colours more than Images as I said many times above. You should make use of float to make the page fit properly on the screen. If you desire you can use smaller font - but beware, don't go below a certain level.
