Ensure your photoshop file is stripped and contains only layers and groups that are used. Make it easy for your web developer.
- Indicate rollover and click states
- Ensure all text is selectable within Photoshop
- Embed all linked files
- Rasterise layers where possible
- Clean up and name all groups
- Convert all vector objects to smart objects
- Supply logos as SVG (separately)
- Include reference files (eg. JPG of each PSD supplied)
- Supply additional notes as required, include font information and font foundry login details where appropriate (eg. Typekit)
Take a bit of care over these files. If they’re clean and easy to work with it helps form good working relationships with developers.