The lights are on
This guide has some useful bits for the more experienced players, if you find yourself lost, look for the beginner guides and those may help you more.
This shouldn't even be in the guide, as basically any experienced player should know about this. focusing is the kill bonus you get when you manage to keep the kill button above your targets head for 1 1/2 seconds. This is not easy, as it gives plenty of time for your target to notice and stun you, but the bonus is worth 150 points. The best way get a focus bonus is to use a disguise to more easily approach your target (this is still hard because the stun prompt will still appear above your head, so it is best to approach the target form behind); go on the roof to prevent being stunned (you will be obvious and your target may try to run out of range); and using a smoke bomb which will make your target completely vulnerable for a good 2 seconds; and of course when your target has been stunned, it makes for a perfect focus (plus a grounded bonus, 50 points, at that).
locking on to your target allows you to do all sort of fancy things. They not only allow you to keep track more easily of your target, they make it way easier to get high scoring kills with out even having your target on in direct sight (for example: behind you). When locking, even when your target is out of sight, the kill symbol will still be above the locked targets head. Let's say you are on a roof, attempting to attack a target on the ground. You lock on your target. Let's say you go for a focus bonus (a good choice if your target is in non-moving crowd) and your target suddenly decides to run away. around a corner. Your lock will remain on them for a couple seconds, and if you are still on killing range, (even if your view of them is blocked by the roof) the kill symbol will still be there, and you will get an easy kill. Always be sure to lock on before you approach your target (or pursuer), it will make it twice as easy to get things done.
When you are playing your favored mode, you may hear whispers in the background. Whispers are signs that an enemy (or enemies) is nearby. Whispers are essential for surviving when you have a lot of pursuers and no abilities to protect you.
This is something only the most skilled players can master. It isn't hard to get, but when the stars align, it can give you a 600 point bonus (extreme variety). Everyone has gotten variety every once in a while, but it's hard to tell what it actually is. When you get certain bonuses (Stun, lure, ground finish, revive, aerial kill, acrobatic kill, grab kill, hidden kill, grounded, reckless, discreet, silent, incognito, focus, etc.), they all will start building up for variety (200), then greater variety (400), then extreme variety bonuses (600).
Variety makes it all the more important to get focus, ground finish, hidden, aerial, and acrobatic; these are some of the easier bonuses to keep in mind, and abilities make it even more doable.
Note that bonuses do not stack (getting 2 focus bonuses will not contribute twice)
If you die, the count will not reset
Variety: 5 different bonuses
Greater variety: 10 different bonuses
Extreme variety: 15 different bonuses
Remember, there are 30+ bonuses, so that gives plenty of options for building up to extreme variety.