You won't get to play Darius very much as he is one of the most banned Champs. When you do get to play Darius - make the enemy team pay. Not much boring stuff in this guide... all you need to win top lane with a little practice. I used to run an AD focused build with Darius and I lost a lot of games. Switching to full tank completely changed my win rate and helped me dominate top lane Note: avoid picking Darius vs Ranged champs.

Pros

Really fun to play & Easy to master
Can dominate top lane
Can carry games
Tank (with this build)
Fun to play and explode enemys with ULT
Good in teamfights (when ahead)
Short Ult Cooldown

Cons

Hard to comeback when behind
Slow movement speed
Ranged champs can hurt Darius

Boots and Sterak's are situational - depending on the enemy composition. Most of the time I run with Ninja Tabi and they work great. Sometimes I swap Sterak's with Guardian Angel.

Q = Poke. Most of the time you will Q them from a distance to get down health.
W = Slow. Very nice slow. Use at end of combo before you get stacks.
E = Pull. Perfect when they are running away.

Darius combo is pretty simple. Just try and get 5 stacks (hits) before you ULT. Poke with Q and AA like crazy to build stacks. If they run, pull them in with E and then slow with W. It looks complicated, but it's not.

Example: Q - AA - AA - AA - E - W - ULT

Important: back off and Q/W if you are losing the trade. ULT should be the finishing move. Wait until they are about 1/4 heath. If you complete the kill you can use your ULT again immediately.

So you won top lane and now are ready for team fighting. Darius can really help the team vs tanks like Malphite. Just remember to use the combo's above and target ADC first. Keep an eye on your health and don't be afraid to go back when you have low health. Going back to base is ok with Darius, dying is not. Most noob Darius players continue fighting too long and end up dying. Unless you are snowballing press the damn B.

Darius is a really fun champ to play in the top lane. I can win most games with this tank build. Hope it helps you too :)