Maybe it's social media updates. Maybe it's occasional blog posts. Maybe it's setting up a mailing list. There are a lot of ways to do self-promotion, and since I consider sincerity to be the most important thing of all, there's really no wrong way. As long as you're comfortable and happy and not drowning in your update links, you're probably okay.
But here's the thing. There is a line between "self-promotion" and "spam," and while that line is usually pretty visible, it's also easy to cross, even without intending to. I schedule Current Projects posts; make Inchworm Girl posts once a week at max; and try to do sales announcements and convention announcements when it will have the greatest impact. It is thus possible—not likely, but possible—that all three of these things could happen on the same day. That would seem a little spammy, and take away from all three. It would also still be confined to my space, which you can read at your leisure, if you read it at all.
The same goes for Twitter. On and around book release day, I get very "OMG BOOK" for about, oh, 80% of my Tweets. I lose a few followers every time I have a book come out, since the rest of the time, my Twitter is very much "here are pictures of my cats and snarky comments about my doll collection." (Most of those followers come back again about a week later, when the book stuff dies down.) And that's fine! I am shouting and running around within my own space, they aren't interested, they go to the corner store for some milk and bread and come back when things are back to normal. This is all totally awesome.
The trouble, for me, comes when self-promotion begins going into other peoples' spaces without being invited. An example:
Last week I tweeted about how my sister is a nervous flier. Within twenty minutes I had received an unsolicited tweet from a retired commercial pilot who does not normally follow me, with a link to his book on calming fears of flying. Now, this may seem like he's just being helpful, but again, he does not follow me, and I did not ask for advice. This is a stranger who clearly has some standard searches coming across my comment and deciding that he can use it to profit.
I told him that what he was doing was spamming, and he asked why I was making such a fuss. The reason is simple: because he came into my space, without my asking him to, and tried to sell me something I had not asked for. He was spamming.
Something I see with much more frequency, although also on Twitter (and, in a modified form, on Facebook), is people @-checking random groups of authors/fans/whatever with "Hey, think about it, Soviet steampunk [link to book]." Again, this is not encouraging me to buy your book, or even to look at it. This is spamming.
It's different when you're doing it in your own space, or when you've been solicited. If I Tweet "What should I be reading?" and you give me a link to your awesome Shakespearean detective erotica, we're all good. If I click over to your feed and it's two-thirds self-promo, that's cool too. But once you come into my space, you'd best be sure you were invited. By the same token, if I'm coming into your space, I'd best be sure that I was invited.
Anything else is likely to turn my serious message into a piece of unwanted lunch meat.