What are some subtle early checkmates or some openings that will win you a lot of material.

scotch game,gőring gambit;sea cadet mate...pretty stuff☺

While it doesn't hurt to know traps in the various openings, going out of your way to focus on them -rather than studying tactics, endgames, opening principles, and strategy is a SURE way to hold your rating down!

I coached some high school kids who would play variations that, if the opponent knew what he was doing, worked out better for the opponent than for the guy trying to spring a cheap trap. I'd try to get them to concentrate on solid play but "My dad [who never played in a rated game] taught it to me and says it works,"

They'd usually win one out of five Swiss Tourney games.  If they stuck around long enough, eventually they saw newer club members who they used to be able to easily beat passing them because the newer members were learning about space, tempo and material in the opening, that a N outpost on the 5th rank was powerful, how to handle a "Bad Bishop," the endgame Principle of The Opposition, etc.  Usually, they got smart and starting catching up on the same things!

In the spirit of my last post, let me say that 1100 or better rated OTB players will NOT fall for most of the traps and often know how to use your out-of-position pieces against you, so against reasonably proficient players you will NOT "always end the game early" - not even half of the time since often the trick works against you.

That is NOT true for the real "gambits" like the Orosov in the Bishop's Opening, the Smith-Morra in the Sicilian, etc. - they blow the game wide open and the person most knowledgeable of tactics and calculation usually wins.  If you learn the tactics most appropriate to those gambits you may have an edge, but before springing them I would study tactics, tactics, tactics and learn their patterns - there are a lot of good videos at chess.com by IM  Daniel Rensch about "Patterns Everyone Must Know" and several videos about patterns in "Intermediate Checkmates by FM Ingvar Johanneson and a very excellent tactics problem setup at chesstempo.com.

Thanks a lot! Who knows how far this piece of advice will get me.

Dissenting opinion here:

Rating points aren't everything. In fact, they aren't very much at all. It doesn't matter as much how well you play as how well you play. It should be fun. Weird stuff is usually fun. It doesn't have to work. Some of the best fun that I have is inviting people to nail me with the Fried Liver. My king is on the dance floor and I'm having a riot. Never boring.

Here are a few that won't make you better but will make you entertaining:

Fried Liver... already mentioned

Falkbeer Counter Gambit, King's Gambit... look for white to capture the wrong pawn.

Old Benoni Defense... Go for the queen's rook in the corner.

Danish Gambit... wild and wooley.

Sicilian Wing Gambit... Have fun stopping black's queenside pawns.

Thanks, I get better every day whilst realizing the endgame and middle game are just as important as the opening