Darius is really easy to play with, because you don't need to build any AD items to do tons of damage. For the first time you leave base, I would suggest trying out Cloth Armor and Health Potion x5 for lane sustain until you hit Lv 5 or 6. Then (if you're solo laning) ask your jungler to gank so you can Back.
Build order should be (after first purchase of course):
- boots of speed (lv 1 boots)
- Vampiric Scepter
- Wriggle's Lantern (from Cloth Armor and Vamp scepter)
- Mercury Treads (from boots 1)
- Heart of Gold
- Maw of Malmortius (From Hexdrinker)
- Brutalizer (either sell it later to get a defensive item, or if you completely wreck shop then build it into Youmuu's Ghostblade, but only if your team (but yourself in particular) are doing so.)
- Frozen Mallet (from Phage)
- Randuin's Omen (from Heart of Gold)
- late game, sell Wriggle's Lantern for a Bloodthirster
- late game, sell Brutalizer for Guardian Angel / Thornmail / Warmog's Armor, or buy a Youmuu's Ghostblade
Runes and Masteries:
- Flat Attack Damage Marks - Self-explanatory. More damage for last hitting and harass in lane.
- Flat Armor Seals. Again, self-explanatory. Helps defend against auto attack damage and minions.However, if you're laning top lane versus an AP bruiser, (and you're in a draft setting and know this before loading screen) I suggest you have two pages for top lane bruiser, one with Armor and one with Magic resist.
- Magic Resist per Level Glyphs. These are for late game to offset some of the magic damage from the enemy AP carry and tank/bruiser/jungler. Personal preference for Flats or Per Lvl, but I find the Lvl MR runes to be the best for top lane.
- Movement Speed Quintessences OR Attack Damage Quintessences. Personal preferences, depending on playstyle. I tend to play extremely passively early game, and prefer more move speed over a bit extra damage, and since its percent-based movespeed, it scales better into late game when you're chasing people down like you've got Boots 3 instead of Mercury Treads.
Honestly, your Masteries will be up to personal preference, as will Summoner spells. I personally go with 21/9/0 and Ignite + Ghost, but again, personal preference. Just be smart and don't build down the AP tree and you can't really go wrong.
** A comment on boot choice **
Many people suggest getting Ninja Tabi on Darius. I would HIGHLY Recommend that you don't, and here's why:
- Movement Speed 2
- 25 Armor
- Unique Passive: Reduces damage from non-turret based AUTOATTACKS by 10%.
Woop de doo, 25 armor. Movespeed 2, eh, you get the same from the other boots. Unique passive reducing damage by a percentage? seems nice... But think about it this way: You're reducing 10 damage off of a 100 damage auto attack. or 100 damage off of a 1,000 damage crit. Now how good does that sound? Not very, huh?
- Movement Speed 2
- 25 Magic Resist
- Unique PAssive: +35 Tenacity (does not stack with other tenacity items)
Magic Resist is okay, but the REAL gem here is that Tenacity. Tenacity reduces the duration of certain Crowd Control effects by 35%.
- Tenacity works on: Blind, Charm, Terrify, Fear, Taunt, Pacify, Silence, Slow, and Stun.
- Tenacity does NOT work on: Knockback, Knockup, Pull, or Suppression.
Generally once the enemy team sees a Darius, they'll want to disable you in some way to make you less effective for at least a short duration during the game, and Merc Treads come in handy more times than I could count, whereas Ninja Tabi I hardly ever get with anyone, because its just not worth it to me since Dodge was removed.
Improving early game in general is easy enough, but hard to pull off thanks to the human factor of the other team. What I would suggest, is whenever you Back to buy items, grab a couple wards and health pots. Ward the little round wall by Baron, next to the Tribrush and diagonally down from the river bush by top lane. This way you see if anyone is coming both up from river and out from their jungle, and you can see if they go into yours. Once you finish off Wriggle's Lantern, you can stop purchasing wards, thanks to its active ability.
While in lane pre-9, I would suggest playing passive and last-hit as much as possible. Don't spam your abilities until you hit Lv 11, because quite frankly, your mana pool is terrible early game. If you're a solo lane versus a double lane, last hitting under tower is the safest place to be. Let your tower hit the melee minions 3 times and the caster minions twice (iirc) before swinging at them.
When you go aggressive, lead with your Q, your spinning blade, and make sure you hit them in the outer edge of it for extra damage. If they run, pull them back in and activate your W at the same time, and make sure you procc it by auto attacking at least once. In between your abilities, always remember to auto attack! You need to stack your bleed passive as much as possible to get the full use out of your ultimate when you inevitably use it.
A word of caution, however: Darius is a detriment to your team overall if all you do is Ult every time someone gets low enough. You need to make sure your team gets kills as well, so you're not the only fed player on your team. While your personal build is probably one of the most expensive ones on your team (besides the ADC) at approximately 14K gold, remember that while you have 5 of your 6 endgame items at 40 minutes, the rest of your team might only have one or two. And its easier to focus one player down (even if its' Darius) than it is four.
Hope this helps you (and anyone else in your situation)!
And remember, summoners: When there's a Darius on the enemy team, Half your health bar is just for show.