Otherwise, I have a standard reply that I just copy-paste in to be human about it and make it exceedingly quick. True, 99% of the messages are not going to interest me, but I think everyone deserves to be treated fairly if they've made an effort. You never know who you might run into a second time when you're in need. It goes something like this:
> Hello [Recruiter],
> Thank you for reaching out, I appreciate it! Unfortunately I'm not looking to make a jump right now, but I wish you the best of luck in finding some great candidates.
> Thanks again,
I'll make tweaks to the standard message when warranted. For example, recently the CTO of a large-ish web property was the one who made the direct contact herself, instead of just a recruiter or hiring manager. I wasn't interested, but that obviously warranted a more thoughtful response. Other times, if the recruiter actually has the wherewithal to (shock!) include salary details and actual information I often complement them on that fact, to encourage the behavior more often in the industry.
In general, true, it can be annoying to get many an unsolicited and uninteresting offers. But on the other hand, what a great privilege we have to be in a field where we are in such demand that people are pinging you left and right; we should count our blessings! :)
Phone - don’t answer unknown numbers
LinkedIn - don’t open the page. It’s generally useless I find. Nobody notices when you don’t congratulate them on their 3 year work anniversary.
How do you which ones are good? Start with ethical. If you ask them to stop spamming you (via opt-out or whatever), do they stop? The ones that do, put them on your list.