It's one of those catch 22 things. If you have to ask how not to make your posts spam, then it will always be spam.
- Make 1-2min videos. Upload to facebook page with the same name as your YT. Promote the post to the same demographic as your YT analytics.
- Make 15s-1m videos. Upload to Instagram. Post 30 relevant hashtags in comment of that post. Promote like above.
- Make 7-15s vertical videos. Post to snapchat. Make the swipe up option be your vid link.
- 90% of your posts should be GOOD value content. 10% can be "asks". An ask is "check out my channel / sub" etc.
- Comment on every post you get.
- Comment on every trending post for the hashtags you use.
DO NOT spam your personal friends with links to your videos. Use the 90/10% rule as above. If your facebook is littered with mostly links to your videos, you're more or less spam. Also, tell your friends once or twice to check out your vids. If they don't start watching on their own, they're not interested. Most people don't like the same things that we do.