What is the best way to promote new initiatives on Steem blockchain without spamming the system but you get the desired exposure and collaboration?
I think that the best way to proceed on Steem is to build it first.
Whether it's a dApp, a community project, or a weekly contest, start it, build it, get it going organically. Get a first version out, get a first few contests run, get a first twenty people in to start the community.
Once you have the project moving then you're in a sound position to "advertise". You need a good sales pitch, explaining what you've achieved so far and how it can help Steem (even if indirectly).
Then the best approach for exposure is to get a launch post out and voted up to trending using bid-bots.
Whilst bid-bots may be frowned upon for "trash" articles, people on Steem are generally much more accepting of projects that are up and running and can be shown to have some value.
Then be patient. Build some more before considering another launch post. Probably at least a month.
I would avoid unsolicited comment spamming or wallet spamming in any form. Those are bad practices and generally just annoy people.
Good luck!