The Mod look is about smartness more than anything else. That means that as time passes the look does change - it's not about looking like you've just stopped off the 1967 bus, although admittedly that's what we'd all like in a perfect world.
So today's mod would look very different from his or her 1960s predecessor, while they both share the same aesthetic heritage.
Desis - aka desert boots. Essential. Although certain other types of suede shoe can be worn on alternate days to keep your desis fresh.
Jeans - the cut will vary depending on the decade. But right now fairly tight is alright. Not too tight though or you might look more of a hipster than a mod.
Jacket - needs to be tailored right. On the neat side. Four buttons.
Parka - get one 9if you can afford it) from Pretty Green or Maharishi both of whom do a great bit of parka design. If not, try the second hand shops for an antique job.
But the shoes are pretty much the most important thing. You could have all the rest of the gear but put the wrong shoes on and your Mod-ness would be vapourised in a nanosecond.
The way to spot a mod. or even an ex mod, is by the shoes. If someone's got on a pair of desis or wallaby style shoes then they're almost certainly acquainted with Mod culture. Eveb the right type of DMs or miltary style zip boots. But scuffed brogues or wellies? Nah.