1. Create a white list of domains or urls exempt from redirecting.
2. Decide to apply "nofollow" to the external link that shows on the redirect page or not.
3. Turn on two-step linking for signature links.
4. Turn on two-step linking for post/profile visitor message/blog links.
5. Turn on two-step linking for user profile/ memberlist links.
6. Define your redirect warning disclaimer paragraph.
7. Decide to use an additional automated meta-redirect or not, and the second delay.
Source: Two-Step External Links for Link Weight Retention - vBulletin.org Forum