No matter the level, the key to all signs is to keep the actual sign as simple as possible. The other complex movements are just a distraction to hide the true sign.
For Catcher to Pitcher signs:
The "classics" are one finger for fastball, two for curve, three for slider and four for the pitchers best breaking ball (be it change-up or "other").
From there, the easiest way to "mix things up" is to simply give two or three signs at once (many times when you see a catcher go out to talk to the pitcher, he's just saying something like "second" to indicate that the second sign of his series will be the valid one.)
For Coach to Batter/Baserunner Signs:
These are the most mis-understood by casual fans because of the elaborate number of moves coaches will put on. Many people think the coaches are communicating whole sentences with some secret sign language. In reality, there are only three important components: The "on" sign, the sign itself, and the "off" sign.
The "on" sign, or "indicator" is what tells the batter/baserunner that the next valid sign is active. Usually there is only one indicator and it's something pretty simple like the coach touching his ear.
The sign itself is a pre-determined instruction. For example: touching the chest"bunt"...touching the belt means "hit and run" ... touching the wrist means "steal"...and so on.
The "off" sign cancels everything and can further mislead the opposing team. Like the "on" sign, the off sign is usally something pretty basic, like touching the cap.
So using the above, let's say there's a runner on 1B and the coach wants him to steal. He touches the following in this order: Nose, Chest, Belt, Ear (indicator), Nose, Wrist (steal), Belt, Leg.
The players see the indicator (ear) and look out for the next valid sign (the nose is a decoy and means nothing, so the next valid sign is the wrist for steal).
Usually, if the "off" sign is given anywhere in the series, there is no play and everything else is a decoy move. So whether the coach touches his cap at the beginning or end of the sequence makes no difference.
The basics are the same for signs from the bench to the base coaches, usually just much less elaborate. They often only involve touching the cap, nose, ear and chin in various combinations.
The key to receiving signs is for all players to watch the entire sequence...The best way for players to "tip" their signs to the other team is to turn away from the coach the second they see the indicator or the "off" sign. This is why many coaches add a couple loud claps of the hands after the sign sequence...this trains the player to wait for the sound cue to turn away.