Be a real, trustable person in real life. Let your real colleagues, acquaintances and friends contact you.

Create an account and let it age.

Seasoned accounts are a positive heuristic in many domains, not just LinkedIn. For example, I some times use web.archive.org to check a company's domain to see how far back they've been on the web. Even here on HN, young accounts (green text) are more likely to be griefing, trolling, or spreading misinformation at a higher rate than someone who has been here for years.