As Andvari said, it's
all about the context, and the specific circumstances. I tend to judge each situation individually, but I'm generally open to most shenanigans as long as the proposed effect is congruent with the proposed action. Small actions get small results. Big results require big actions. The limit is pretty much when something starts to seem ridiculous to me - if you want to try some Daniel Craig James Bond stuff you can roll for it if the basic idea sounds at all feasible in that particular situation, but Mission Impossible-level stuff is probably not going to fly and anime or cartoon crap is right out. No sticking your finger in a gun barrel to keep it from firing - but a rock
might work.
If you want to use your bonus action or reaction to throw sand in someone's eyes or a drink in their face to try to gain advantage for the turn or give them disadvantage, roll for it.
Assuming there's sand where you are, or a drink within reach.
Holding onto the edges of your cloak when you jump off a building is
not going to help you prevent falling damage, but if you're trying to jump across to a rooftop
lower than you and by RAW the distance is out of your reach
by less than ten or fifteen feet, I'd let you make a roll to attempt to use your cloak to get a little extra hang time and alter your trajectory. Expertise in Athletics or Acrobatics? Roll, schmoll - go, ninja! (But you're
still not Batman, lol.)
In the case of magic spells, I'd look at both the levels of the spells involved and at
what the spells actually do in terms of physical effects.
As for bouncing a lightning bolt off a mirror, I'd rule that you could
try to deflect it off in a different direction, but whether you succeed or fail at that, you're still going to have to make your save against the damage.
For the example in the movie, although you could quibble about the fact that one of them is an object made solely of force energy vs the other actually being physical, the idea that you're basically trying to engineer an arm-wrestling contest is fairly sound.
Considering that the spells are only two levels apart, I'd probably rule that the winner of an opposed contest between the spells (maybe each spellcaster has to roll against the other's spell save DC? Advantage on the roll for the higher level spell?) gets to function normally on that turn, basically like a runner breaking through the scrimmage line at a football game. Once the deadlock is broken, if there's still time left in the spell duration and the spell effect is either moveable or still in range, whichever caster lost the contest could try to re-engage on their next turn.
On the
other hand (pun intended), no
first-level spell is going to have a non-RAW effect on a
ninth-level spell - if one of them was using the
Mage Hand cantrip to try to go all I-know-kung-fu on a
Bigby's Smashing Fist, that's semi-truck vs. squirrel territory right there, and it ain't happening...
