• All page layouts need to follow the tips as stated in this post Usability: Fields and Page Layouts. Except record Owner to be top right hand corner.
• All page layouts should be consistent in layout as much as possible.
• Page layouts for different record types need to be very consistent. I think it is easiest to do these layouts at the last minute. Create a master layout with all the fields on it, then save that for each record type layout, and remove the fields that are not necessary for that layout. Also, have as few page layouts as possible, because it is a pain when adding new fields to add them to every page layout. 
• Never add a new field to a page layout automatically, I can guarantee you that you will never want it to be the last field in the left hand column in the first section. 
• All sections must be shown on Detail Page and Edit Page except for where you use a hidden section to show 2 column and 1 column layouts in the same section. 
• System must be the bottom section and have the Created By and Last Modified By in in. 
• Don't add too many Admin only or Report only fields on the Page Layout (As suggested in How to create an Admin Page Layout), use the really cool Browser Extensions for Chrome, Grey Tab and Salesforce Inspector to see underneath the hood. 
  • If you do add them, add them to the System section so that users can safely ignore them. 

A Warning

Page Layouts can get quite cumbersome. Take for example Cases - you want different layouts for different profiles, then different layouts for different stages of the Case process (eg the support team should put the case through to an Admin for Approval where the Admin can see some key info about their account status. The Accounts team just see basic info about Open cases). See the example in Building a "Simple" Case Management Process.

So very quickly you have quite a number of Page Layouts to modify. The only real way to keep track of these is using the ideas shown in MavensMate and Git for Non Developers.

See Also 

• Page Layouts