The major limiting factor in DSI is the scanning time. DSI usually takes a very lengthy scan to achieve good quality, and the most of the principles aim at reducing the scanning time and improve the image quality. Here are some rules I concluded from my personal experiences, and it may change case by case, especially a difference pulse sequence is used to acquire DSI.
1. Use shortest possible FOV, TE, and TR
Shorter TE has less distortion, less scanning time, and less T2-shine through. Shorter TR also reduces scanning time. A small FOV may also improves a bit in getting shortest scanning time.
2. Isotropic resolution, i.e. in-plane resolution = through plane resolution
This aims at getting a good result in fiber tracking. Diffusion fiber tracking is non-isotropic resolution is problematic, and not recommended.
3. Acquire at least 100 diffusion weighted images
My personal experience. Acquiring less than 100 directions may not be able to achieve enough angular resolution.
4. Use grid sampling scheme.
5. Consider ignoring cerebellum