Consistency is probably the most important consideration. If the exit button is in the top right corner on some forms and the bottom left on others, people will be constantly clicking in the wrong place and if you have a different button there, then that's what will get pushed or they get frustrated by having to search for something that should be in the same place on all forms.
Minimize the number of colors and fonts. Choose a color scheme that red/green color blind people can still use. Some companies like their forms and reports "branded". Figure this out early on because it is a royal PITA to have to change this stuff after you've created dozens of objects. Spend as much time as necessary with the first few forms to get a pattern you can use for all the other objects.
Use Themes rather than hard-coding properties. Be careful though. Themes are not interchangeable due to the differences in font sizes.
Use the user's terminology. If they call some entity a Customer, don't refer to that same entity as a Client and especially don't vacillate between the two terms.
Web pages drive me crazy because they are so filled with pictures and white space and require constant scrolling. I HATE to scroll. Design your forms so that they fit in the standard screen the users have. If you have multiple screen sizes and resolutions, go for the lowest common denominator or buy a tool such as Shrinker/Stretcher by Peter's Software. Access does not provide good tools to handle screen size/resolution differences. You have to find a happy medium between density of information and readability. Tabs can make this easier.