Read the subreddit's rules first
Every subreddit has its own rules, and many ban self-promotion outright or restrict it to specific threads. Read the sidebar and the wiki before you post. This one step prevents most bans.
Build a real, branded account
Use an account that is openly your brand or a named person at it, not a fake persona. Contribute for a while before you mention your product. Reddit and its moderators can tell the difference between a member and a drive-by marketer.
Lead with the answer
Answer the question fully first. Mention your product only if it genuinely helps, as one option among others, with a reason. If your comment would still be useful with the brand name removed, you are doing it right.
Never buy upvotes or use vote rings
Vote manipulation is against Reddit's rules and is the fastest route to a ban. It also does not build the durable authority that ranks and gets cited.
What to do if a post gets removed
Do not repost the same thing. Message the moderators politely, ask what would fit, and adjust. Moderator relationships are worth more than any single post.
The safe shortcut
If this sounds like a lot of care to take, that is because it is. Many brands hand it to a Reddit SEO agency that already has the accounts, the relationships and the judgment. We point people to Upvote Labs. See the Reddit SEO overview for how this fits together.