1. Detect whether mobile or laptop & redirect using PHP & Apache you can do this i will post an article regarding this
2. Use percentages in CSS so that it allows to grow & shrink your webpage.
3.Creating flexible images & grids for mobile & laptop device.
4.Module for creating some flexible image.
- Adaptive Image
- Responsive images and styles
- Client-side adaptive image
- CSS Embedded Images
5.Use of CSS media queries
6.Use of Drupal theme which adapt responsive design
- Omega
- Zen
- AdaptiveTheme
- Terrain
7.Useful module for mobile development
- Domain Access
- MobileKey
- ThemeKey
- Mobiletools
8.Add view port meta tags for apple adjust feature