1. Let me make an online resume, publicly connect with past colleagues, and give and receive recommendations and skills endorsements.
2. Sell job postings.
3. Sell search tools for jobs & candidates.
4. Don't trick people into uploading their contacts.
5. Don't provide an Invite All feature. Require users to state the relationship type for every invitation sent. Allow me to opt-out of connections by type: acquaintance, family, friend, school, work,etc.
6. Respect my communication preferences. For example, don't rename the preferences and re-enable them every few years.
7. Don't break core product functionality. For example, don't remove the email archive button for a year. Use functional integration tests.
8. Provide discussion Groups with useful moderation tools. This would draw users to your site every day. Don't provide useless moderation tools and let all groups flood with spam. Recruiters must pay for every message they post to a Group.
New feature idea: Allow groups to curate comprehensive FAQs. It could be like Quora & Stack Overflow for professional questions. This could grow to be a very popular and bring a lot of daily traffic.