Various questions that may not be answered by the above guides, but are still asked often:
How Can I Increase My Power Level?
Your Power Level is calculated based on your F.O.R.T. stats, which come from two sources: Survivor Squads and Research Levels. While Research Levels are time-gated and can only be progressed when you have enough research points, Survivor Squads can be a quick way to readjust your Power Level. The in-game auto fill feature will do a good job for you at the start, but it's best to match the squads manually for optimal results. Refer to the guides above for how to do so.
Ventures is seasonal content which allows Commanders to re-experience level and experience progression for great rewards. Read the announcement blog post here. The current Ventures season is called Scurvy Shoals. While geared toward end-game players, it offers content for all levels all the same.
The current Ventures season will end June 19 at 8PM ET, unless changed by Epic Games.
They like to "hide" in a bit more obvious spots than typical chests, as they "want" to be found (i.e they aren't in the tops of houses, but instead out in the open).
Outlanders have a perk called "Keen Eyes", which triggers after 5 hits with a pickaxe (i.e harvesting a tree). This perk highlights containers (chests, searchables) that contain valuable objects but it does not highlight mimics, so you can tell if a level 3 chest is a mimic with an outlander if it doesn't sparkle with Keen Eyes.
While Dungeons are active (Good news! they're currently active) you can find mimic spawns in each of the dungeons. Here are a few youtube guides: The CryptsThe InfernoThe Grotto