Realistically, the main thing to increase the probability of the papers coming out of your conference being taken seriously is to:
- Convince a professional organization such as ACM, IEEE, or USENIX (to provide some examples for Computer Science, your field will surely have similar organizations) to print the proceedings and include them in their digital libraries (if existing), or
- Partner with a reputable journal to print your proceedings as some recurring special issue, or
- Have a really high-prestige organizing committee back your conference and vouch for the quality of papers.
In short, you will, unfortunately, need to piggyback on the prestige of some other entity (a publisher, a journal, or a bunch of well-known individuals) to get your proceedings off the ground.
To answer your specific suggestions:
Would it help if we assign DOIs for each paper and/or the conference proceedings? Does it matter which?
DOIs are cheap, and even many spam- or borderline-spam journals happily assign DOIs. I can't imagine this being seen as a seal of quality.
How do we improve search rankings on google scholar?
IIRC search rankings on Google Scholar are a combination of citations and match of the paper to the search query. I don't think there is much leeway to game the system (aside from citing previous papers in the conference, of course - but thinking this thought through to its natural conclusion quickly ends up in rather unethical practices).
How can we get the proceedings included in scopus?
I have little knowledge about Scopus given its low relevance to Computer Science in my area, but to the best of my knowledge they don't index proceedings at all?
I should also say that nowadays the barrier for national conferences (and if I understood your question correctly yours sounds like a national conference) to be taken seriously as a prime publication venue is extremely high. There is an abundance of international meetings to choose from, and most researchers choose those to publish their novel and exciting new results. National conferences are really meetings, first and foremost, not places to publish new results. Some of the more prominent national meetings in Computer Science have moved away from printing proceedings altogether, and focusing on what a conference should arguably be about in the first place - to present and discuss ideas and previous work, not to publish new results.