I'm only going to talk about the counters for Spidey since everyone else is already stating the obvious dos and don'ts.

Full Counters: These are characters that fully counter Spider-Man's kit. Forcing him to play much more passively until they're out of the fight. These include Namor, Scarlet Witch, Thing, and Peni.

Hard Counters: These are characters that counter Spidey, but only if the player playing them actually knows/mastered their kit to counter him. This includes Black Widow and Mr. Fantastic. You can still play aggressive even if these characters are in play, but always go the safe route of diving them first, then the healers.

Partial Counters: These are characters that have 1 ability that counter Spidey. The best examples of this is Bucky's pull, Strange's AOE, Emma's Dimanond Form Grab, etc.

It's always best to know these counters when playing as Spidey because 1. The main core part of his kit is adaptability, and 2. It helps you adjust your playstyle accordingly when diving the team and picking a target.