I use the optional facing rules from the DMG when I run games in a VTT that makes it easy to keep track of (TaleSpire for example, allows you to rotate minis)

Basically, the rules are that you have advantage when attacking the back hemisphere of a creature. A creature may use their reaction to face another direction when another creature moves. (I allow that rotation to continue throughout the attacking creature's turn to prevent players from moving a bit, to get enemies to face them, and then moving again after the enemy has used their reaction -- yes, there are players who will do that because they see the DM-player relationship as combative rather than as collaborative storytelling)

Shields only give the AC boost to the side that they are equipped on

Prestidigitation is one of those spells that are more flavourful than impactful until the very moment is absolutely perfect and everyone is staring at their character sheets in a panic wondering what the hell they can do in a clutch situation.

Until then there are plenty of things you can do with it for fun and to encourage roleplay (depending on the style of table you're at): flavour someone who just upset you's food like something gross, snuff out the candle of your wizard copying spells in the middle of the night because you don't sleep well with a light on, sneak up behind someone and add to the fright when you say, "What are you doing?" by making an explosion of sparks.

Talk to your DM so that you both understand what each other are going for, but you will probably find that a lot of DMs are far more lenient about these things if they're used as flavour rather than for tactical advantages.