Are there any common tactics or combinations used to beat complete beginners quickly (or gain large material advantages)?
By "beginner" I mean someone who is good enough not to get caught out by Scholar's mate, and knows basic opening principles, mate with king and rook etc., but not any actual openings.
As T.S. Eliot said, "There is no method but to be very intelligent." If the opponent is smart enough to avoid the known short mates and understands basic opening strategy, you'll just have to outplay them.
That said, in my experience, new players often miss forks, discovered attacks, and moves that theoretically place a piece under attack, but where the capture would result in a check or expose an attack on a more valuable piece. New players are often so focused on protecting the king and/or queen that they blunder away pawns and minor pieces by leaving them vulnerable to such moves.
My advice: play better than the beginner and you will rapidly overwhelm them and find blunders to exploit. :)
Simon Webb's book Chess for Tigers may have many flaws, but one thing it does very well is its description of how to deal with substantially weaker players: "[...] regard his whole play as one big weakness."
If you are much stronger than the opposition, then they will make moves that you recognise as mistakes but they don't. I'm not talking about tactical mistakes, but simple things like putting pieces on squares where they don't do anything or weakening pawn moves or whatnot. Just keep the position fluid and the errors will come.
I agree with lots of the advice given here but feel compelled to recommend you try some gambit openings against a beginner to try for quick wins.
Gambit openings are generally quite confusing for beginners who usually cannot resist taking freely offered material (often pawns) and then find themselves under pressure after rapid piece development with mate threats (often focused on weak squares such as f2/f7/h7).
There are many gambit openings available (and they can be more effective in blitz chess when there is limited thinking time). My favourites are: Smith-Morra gambit/Benko gambit/Budapest gambit/Tennison Gambit/Evans Gambit/Scotch Gambit/Danish Gambit/Cochrane gambit/Hennig-Schara gambit and even more dubious ones (eg Blackburne Shilling/Latvian/Elephant gambits etc etc) and even more subtle ones (Milner-Barry gambit in French defence). There are too many to list! Find one you like in your favourite opening and try it..it is usually a fun way to play.
Beware though your opponent may only fall for the gambit one time..once bitten twice shy! Enjoy your gambit play but go easy on beginners..they need some encouragement and not getting hammered in next to no time! It can be more challenging playing gambits against better rated players!:-)
Usually when I play beginners who are beyond falling for scholars and fools mate and can do the basic checkmates; I just play like I always do, making logical moves and just playing them as if they were any other opponent. I never underestimate them.
Usually, after a few moves or so, they will make a tactical or positional blunder. Basically, I just wait for them to commit Hara-Kiri (suicide), nothing more than that.
Launching a kingside/queenside attack is also quite effective as beginners will usually panic in the face of the oncoming pawns and will blunder in such positions, being unaware of the various defensive and counterattacking methods.
Beginners are also usually unaware of endgames any more complex than the basic checkmates so you could just keep simplifying into an endgame where you have an advantage which they are unaware of such as a protected passed pawn, superior Knight vs bad Bishop, Rook on the seventh/second etc.
Any opening that has typical middle game positions will do:
Queen's gambit declined-Exchange variation, openings that have Isolated Queen's Pawn ( QGA, Nimzo Indian defense... ) and so on...
He may know "knights before bishops" rule, he can learn 30 moves of theory pretty fast, but to play these middle games well, you need overall experience and you need to know typical plans for both sides. Your superior tactical skill, and greater experience in positional play will inevitably triumph.
You could also play symmetric position and outplay him by transposing into better endgame. They do not know how to recognize bad piece from a good one, so if they have an equal number of pawns and pieces they usually exchange. Use this fact to transpose into "good vs bad bishop" endgame for example.
To beat such a beginner, I would use "tricky" openings such as the Sicilian defense (c5 vs. e4) or Dutch Defense (f5 vs. d4) as Black. And Reti Opening nf3 or English Opening (c4), as White.
Your beginner is probably familiar with center pawn openings (and related piece development) but likely to lose his/her way in openings where your center pawns are held back and your pieces thrust forward.
Play less usual non book lines he would have memorized. Be aggressive. VERY aggressive. Wait for a mistake. Then crush him. And if no 'mistake' you should have a winning attack. Maybe worst case you win an easy end game.
Myself, I would prefer to play to be sure to win rather than risk not winning by trying to achieve that win fast.
Try controlling centre portion of board with maximum pieces rapidly.
