This is my take, born fresh from my head in the aftermath of a discussion with Slarty.
The warlock who has the best strategy usually wins in the long run.
Certainly individual matches are decided on tactics, and having a library of sophisticated tactics to use will tip the balance in certain games and increase your winning percentage still further. But not all 'master' players were/are tactically sophisticated. ExDeath and Yaron were, and perhaps it's something you need if you want to be among the very very best, but knowing exactly when to go for a Time-Stopped FoD will win you more style points than matches.
Now the problem with strategy is that it is a changeable thing. In a recent game, I'd gone Invis while being hit with an Amnesia, but had a goblin attacking my opponent. At almost full health, taking two damage to go Invis himself was cheap, and the best defence against my Invis. If his attack was devastating enough, he could ignore the goblin and kill me before it killed him. More likely, the fear of facing such an attack would lead me into a position where I was ripe to be picked off with double Charms, say, and any monsters of mine would transfer ownership. For the sake of that two damage though, he delayed long enough to pick off the goblin, lost the chance to go Invis, got Antispelled and then was unable to stop me from gaining an ogre and putting the pressure on. That ogre stayed with me 21 turns, disrupting him much of that while, and did 6 damage; it won me the game.
Clearly, going Invis is worth taking two damage for.
... except, of course, if you've got seven health, and your opponent has the same or more and is likely to storm.
And that's what I mean, strategy changes. In the early game, you may need to accept a little damage to get a position you can dominate from, but knowing just how much is a bit of a delicate thing. Generally if you're dropping down to equal health with your opponent but gaining the initiative, you should go for it, and this remains true up until the point at which one four-gesture spell can pick you off, the deadly five points.
There are simple axioms to remember, but most of them at some point prove false. Clapping ruins your spellflow, don't clap if you can avoid it. Protect your monsters, because they will do a lot of your work for you. Resistance is useless. And every single one of these at some point requires a "but".
Some key generalizations are, I guess, if you don't have a plan in mind to significantly harm them: make sure if there's a monster, it's on your side. If that's done, it's usually good to charm people. In fact it's so good to charm people that you often, even usually, see top players continuing WP as WPS rather than going for WPFD. Taking cheap damage is usually unproductive early in the game. And just as you wouldn't open with damage spells, you don't let an opponent hit you with disruptions and summonings to make them lose a few health points when health is near full on both sides.
It's making these axioms basic to your play that makes you a high-percentage player. The next step beyond that requires knowing when not to be a high-percentage player.