How good of a conference can I realistically submit my first paper to? How can I figure out which conferences I'm good enough to submit to?
You learn to evaluate these kind of things by experience. You read the papers published in the conferences, form your own opinion of their quality, see how they impact the field over time, see how they are viewed by others, and revise your opinions. Eventually you get a general sense of how "good" a paper should be in order to be published in this conference, and you compare it with your evaluation of your own paper's quality.
You bootstrap the process by drawing on your advisor's experience.
So: Ask your advisor.
Asking your advisor, as suggested by @NateEldredge, is a good first step and many advisors will be able to help you. In some cases, though, your advisor may be unfamiliar, may just not publish much any more (that was the case for my advisor), or may not be able to effectively help for other reasons.
If this is the case, then I would suggest two other methods for figuring out where to send your papers:
- Look at the papers that have been published in previous years, and see how their scope and quality compares to yours.
- Aim high, and see what kind of feedback you get back from the reviewers. The worst that happens is that they reject your paper.