1. BUY PRIME ACCOUNT (VERY IMPORTANT) - Even Valve said it has huge impact on your Trust Factor !
2. USE STEAM GUARD (VERY IMPORTANT) - It tells Steam that your account is more trustworthy !
3. PUBLIC STEAM PROFILE - (NOT IMPORTANT) - It's just privacy setting
4. REPORT CHEATERS - ( VERY IMPORTANT) - Help Valve clearing games from cheaters
5. REPORT TOXIC PLAYERS - (VERY IMPORTANT) - Make community nice and friendly
6. WATCH OVERWATCH DEMOS - ( VERY IMPORTANT) - point 4
7. DON'T KICK PEOPLE FROM YOUR TEAM - (IMPORTANT) - Kick only obvious hackers and people who are griefing games
8. DON'T USE CHEATS - (VERY IMPORTANT) - If people report you, your Trust Factor go low
9. DON'T BE TOXIC, BE FRIENDLY - (VERY IMPORTANT) - If people report you, your Trust Factor go low
10. BE ACTIVE STEAM COMMUNITY USER - (IMPORTANT) - Increase Steam activity
11. ADD MORE FRIENDS - (NOT IMPORTANT) - Steam doesn't care about your friends amount
12. RATE GUIDES AND AWARD THEM - (IMPORTANT) - it's the same point as 10, just increase Steam Activity
13. COMMENT ON PEOPLE'S PROFILES - (NOT IMPORTANT) - Steam doesn't care about it
14. DON'T BLOCK AND DON'T SHOOT YOUR TEAMMATES - (VERY IMPORTANT ) - don't ruin games
15. GET PRAISE (HONORED) BY YOUR TEAMMATES) - (IMPORTANT) - It tells Steam you are good guy

So basically - you don't need to add friends, comment profiles, have public steam profile. You just have to be a good person :) Report cheaters and toxic players, be nice and friendly, help other people and be active on Steam Community by rating for example guides :)
I follow this rules and I have very good Trust Factor.