I have been on the support team for MyBB since December 2008 and have dealt with thousands of users, threads and issues. Over that time, I've come up with some handy tips on how to ensure your issue is resolved as quickly as possible.
Use vague thread titles
Titles such "help me", "problem", "not working" or "how do I do this" will guarantee that your thread gets looked at sooner by as many people as possible.
Give no information
The less information you give, the quicker it is to help you, because we don't have to waste time reading. We don't need to know the URL of your site, version you're running, information about what's broken or not working, or what you've already done to try and solve the issue.
Don't answer questions or listen to suggestions
If someone responding to your thread asks you a question or suggests something to try and fix the issue, ignore the question and refuse to accept that what's being suggested is correct. After all, you know better than the person helping you, right?
Ignore sticky threads
Support staff will often create sticky threads for common issues, with information about how to solve the issue without you having to ask, however reading these will take you more time than creating your own thread, so do that instead.
Searching for other threads about the same issue only wastes your time - it's much easier to just post your own thread!
Cross / duplicate post
Why create just one thread when you can create three? Even better, post links to your threads in other people's threads to maximise exposure - it's even more effective if the thread you post in is nothing to do with your issue.
Bump your thread frequently
If you're not trying to bump your thread at least three times every hour, are you even asking for support?
Old threads are often super relevant to the issue you're having today - in fact, the older the thread, the better.
Private message staff members
It's always a good idea to PM a link to your thread to staff members as you'll get an answer quicker - it's even better if you send it to multiple staff members, or even non-staff members too.
Report your thread
Even better than PMing staff members with a link to your thread, is using the post report feature to alert them even quicker.
Edit original post / don't post solution
If someone helps you solve your issue or you manage to fix it yourself, make sure never to post the solution, and always remember to edit the contents of your original post to "nevermind, fixed", with bonus points for changing the thread title too, to ensure nobody else can refer to the thread in future.
If you do as much of this as possible, you'll be sure to have the best experience possible with your support request :)