Do you think your PC could fight a vampire and win? If he fought cleverly? If you do, try and describe that, and if you describe it cleverly the DM will let you get away with it...but try to write it so that you hold and
advantage, rather than have
won. That way the DM can decide the outcome, but you've helped him make a decision.
Same if you're at a disadvantage; don't suddenly put yourself in a winning position, but write yourself out of the disadvantage.
Of course, when chased by a units of dark treants, you should know that running is for the best...but nothing prevents you from writing in torching few of them along the way
(I'm actually pretty fond of diceless or near-diceless RPGing...)