Yes, that is absolutely the way to do it.
There is a question as to how effective self-promotion threads are. It can be difficult to get clicks, but I can say I discovered some hidden gems I'm not sure I would've found otherwise.
As to whether or not it's "polite". Well. I have seen people silently link their comics seemingly without even reading the thread (i.e. "link your own comic and rec another" and they only plug their own).
Other than that, I'd be a hypocrite for saying self-promoting bugs me, hah. People are just excited to share their work.
I sometimes forget to go back and look lol. But i usually see the same people in the same thread so somewhere in there i get to reading their story. Also, i think it's more beneficial in the long run to genuinely sub to someone's story if you're actually going to read it. I appreciate the help but i'd prefer actual readers or even people who'll like my chapters when i update. It makes no sense to come here to get like 50 subs but only have not even a quarter of the likes, you know?
My rule is once per thread. If a promotion thread is new, I may add again. BUT my favorite ones are where you "read for read" or "sub for sub" because I've found new friends AND new comics that way. I mean, it's not impolite to just post the link, but it's really fun when I can privately message someone, or even just comment on their work and gush about what they did well!
I'm going to speak to novels for now:
Daily, no. But if the topic applies to your novel and you have something more than just a link to give, I think it's okay. I've actually gained readers from posting my link here. I've never promoted elsewhere and the forums have helped me there.
But posting over and over again in every topic that you think pertains to your work can get tiring ALONG WITH the same topics. It tends to dig up old topics that were ready to rest.
Novels seem to be a doomed category for repetitive topics like "Post your novel here" "I'm new, here's my novel, post yours" or "Post your novels under 200 subs".
It's nice when there's actually an in-depth topic to work with for novelists.
I think the same about subs, having a caring fan base that actually reads and comments is the best thing about this web.
By the way, I want to reiterate what @Rhonder said about the link in the bio. I usually check them constantly! Actually I feel I'm missing a lot of comics of this thread.
This one is kind of an interesting subtype tbh. I do think it's appropriate most of the time to make a forum post announcing a new project like that, but you're right that often times they're like "oh but you can also put yours too!" which... I dunno, seems unnecessary in some ways? If you're gonna direct attention to your own project give it room to shine imo! There are numerous other link dump threads without turning one's own soap box into one 
I need to go add mine and i never would have thought to do that.
I like threads like this because these forums aren't always about post dumps, but actually talking with other people and helping each other out. I actually haven't posted my link much today, I've spent it mostly talking to people
I think this is why a lot of people see them as spam..! Because the threads have become drop and go instead of people hanging around to chat and ask questions about each other's content. In and of itself it's not necessarily spam, but it can definitely feel like it when you see it over and over!
Engaging with others is always a lot better than spamming a link I think. I really like mutuals because it creates a better dynamic for engaging vs. following a bunch of people I don't feel a connection with. I've made so many friends in the comic community this way, and found a lot of great comics I'd never have looked at otherwise just because they wouldn't have appealed to me on a description only basis. I highly encourage others to engage vs. just posting a link and running as well since it's through engagement that connections and friendships are made 
As the creator of the greatest sub thread in all of history (including but not limited to all the multiverses)...
I feel I should note that it's also a question of most of us not being really great at pitching ourselves/our projects. We just post a link in these threads then silently slink away.
Where's the showmanship?! The Razzle Dazzle!?!
Maybe we should burn the approach down and rebuild it from the ground up!
I've seen a couple attempts where you have to give feedback/sub back, but not very much. I'd LOVE to see threads where it's in the rules that you should interact/reply to at least one person and start a conversation. Maybe you find a new comic/novel you like, maybe you make a new friend, maybe both!
Spamming isn't really worth it imo. It's awesome to share your link in a thread that calls for it from time to time, but I don't think you can gain much from mindlessly spamming it everywhere. I think posting meaningful things and holding interesting conversations with other members is much more effective in my experience.
Mmm yeah, I feel like people more likely to checkout longer promotions with their artwork and info on their comic. gotta stick out from the links. Is why I started leaving an animated picture from my comic when I'm on these promotion threads.
I've found the most effective way is to never share your comic in multiple "share your comic!" "comics under x subs!" threads all at the same time. You need to spread it out, because different people are on the forum at different times or on different days, and spamming comes across desperate and pathetic, like you're unable to get readers, which will make people perceive your comic as "low demand" or "less good".
Prioritise threads where you post sample pages. I pretty much never miss the "post your latest page [month]" threads; those threads are some of the most useful; a page is worth so much more than a description (I also frequently have found new comics to read on those threads). Threads where you post things like work in progress to finished pages or pick out the funniest or coolest page or funny panels are also great. They're more effort, but that's the point. Minimal effort copy-paste spam posting the link and a blurb in a bunch of threads all at once, then being completely silent the rest of the time and posting in no other threads is highly ineffective, especially because most people on "share your work" threads are only there to promote themselves.
I don't spam at all. In fact, I barely advertise or promote my comics after the first few times I've been on this forum.
Whenever, I post in a thread like this or this, I always tell users to refer to my profile instead.
That way, I can stay humble and continue what I want to do without gaining much subscribers.
And yeah... quote...
Wow, as i'm for another time-zone i didn't see this coming xD (it took a while to read all of your resposnes^^')
As she said:
@WolfUnderTheMoon89
This was an enlightning thread, thank you all for that!
I'm glad then that I was pointing to the right direction 
Thanks you all!