One of the first elements to consider in any game of Secret Wars is what Tier your campaign will be staring at.
Generally, a story will either stay in one tier over its entirety, or its tier will escalate alongside its stakes. It's very unusual for a story to actually decrease its tier, as that involves decreasing the scope of a storyline. Heroes used to saving the world from Eldritch gods from beyond the stars might find investigating a haunted house to be a bit rote, after all.
The following represent the various Tiers of Secret Wars.
Tier 1 stories are generally local in focus, typically centering on a small town, or a neighbourhood or community within a larger city, and the mysteries therein. Characters are typically new to the whole "heroics" business, and might not have any connection to the larger forces at work within the universe. At this level, the heroes and the threats they face are just too small for the powers that be to notice; though that doesn't mean that they're not important, especially to others in the community who are unaware of the threats that lurk in the dark.
While most Tier 1 heroes are humans encountering the supernatural world for the first time, it is possible to have supernatural characters active at this level, especially those who are only experienced with their own little corner of the secret world. Examples could include:
A werewolf fresh off their first change, trying to understand their supernatural nature
A horror who's been given their first haunting assignments and are eager to build their legend
A witch who has just started practicing real magic after finding a grimoire buried in an attic
A recently raised vampire who's been given a backwater, undesirable territory to hunt by the local Powers-that-Be
In truth, any rookie supernatural can fit in with Tier 1 adventures, as most only know a sliver more of the occult truths of the universe than their human neighbours. A witch or a werewolf who's never had to deal with a haunted house before is going to be just as shocked as a human when the force possessing the building turns out to be demonic instead of phantasmal.
Inspirations for Tier 1 stories include: Twin Peaks, Supernatural, Gravity Falls, Silent Hill, Eternal Darkness, Hunter x Hunter
The heroes of Tier 2 stories are typically involved in some way in the Secret War itself, usually as members of one of the Secret Societies. Tier 2 stories are usually regional in focus, though they can vary in scope from a single town to a globe-trotting adventure. Heroes are usually more knowledgeable about the supernatural world as a whole, and have more resources to pull on than local heroes, even if they are fresh recruits who in their first weeks on the job. Adventures at this level are usually tied into maintaining the Veil, or larger-scale occult threats that have the potential to cause significant harm to the world--physically or metaphysically.
Tier 2 adventures are more open to non-human heroes, beings who have grown up in the secret world and have lived their lives on the sidelines of the Secret Wars. Depending on the adventure, it might be apt to have all the members of a party be members of the same Secret Society (such as the Blackcloaks), or it may instead work well to have heroes be representatives of several Secret Societies, thrown together by some greater threat.
Inspirations for Tier 2 stories include: The X-Files, Torchwood, the Librarians, the Laundry Files, Angel, Hellboy, Hellsing, Men in Black, the Secret World, Resident Evil
Tier 3 stories involve truths that the lower tiers were only dancing around: the Earth is currently undergoing a Dark Tide event, a period of heightened magic and overall weirdness. Ancient ruins are humming back to life, old magics stir again, and ancient gods walk our modern streets. Things are about to go sideways in a cosmic fashion, and Tier 3 stories put the heroes right in the path of that action. Heroes at this Tier rub elbows with entities such as archangels, bogeymen, fey gentry and demon princes, and nobody bats an eye. They get drinks with Hercules, Merlin and Dracula in Inari's pub. They are well on their way to becoming legends in their own rights.
Inspirations for Tier 3 stories include: American Gods, Good Omens, the Dresden Files.