1. Flanking – If two allied characters are positioned on opposite sides of an enemy, then both of those allies get advantage to any melee attack rolls on that enemy. Yes, rogues can sneak attack this way.
2. Creative use of spells or abilities – I generally view your character using spells or abilities as more of an art than a science. If you want to perform some kind of creative alteration to a spell or ability, for example altering “gust” so that it pulls a creature to you rather than away, or using thieves tools to try to fix a clock. Then feel free to try.
You will normally have to roll some kind of skill or attribute check whenever you try to alter a spell or ability in such a way. The more drastic the alteration, the more difficult the check. And if you fail, there could be consequences (gust knocks you down by mistake, fireball explodes in your face).