Dragon Knight is a tanky carry/pusher that exels in the mid game but can semi carry well in the late game.
If you are going for a pushing strat this should be maxed first since it is a spamable ablility to quickly nuke down creep waves
This is the first ability you should skill because it is the longest level one stun in the game but you should not level it past that since it is also the worst scaling stun in the game
This is leveled early in the farming build because it will make it almost impossible to force you out of the lane the armor is also very good for the pushing build for increased survivability
This is your most important ability for the pushing build you should not level it up until you can get your level three ultimate because once you level it pass your level one ultimate you will lose your extra twenty damage over time to towers and unless you are stacking to farm ancients the small AoE damage the level two ulti provides is not worth much on the other hand if you are doing the farming build you should be using your helm to grab a creep to stack ancients so you should skill your level two ultimate and durring the late game you do not want to team fight unless you have your ultimate since ur ability without it is severly hindered
Get the tangos and salves for some regen early in lane the branches for some more damage to last hit in lane and the stout shield will help you take harass in lane
For the pushing build you get a soul ring to burst down waves and harass in lane since your passive regen will let you use your soul ring every time its off cooldown. If you are going for a more farming carry build vanguard is good to make your already tank hero very difficult to kill
Armlet is an all around good item for DK giving him more damage and HP. Treads would be the best boots for DK because of the attack speed and stats they give you. Helm of the Dominator is a good pick up if you are going to get armlet since the lifesteal will negate the passive damage you take from armlet you can also use it to control a creep to stack ancients if you take your level 11 ulti to increase your farm substantialy
With BKB and Pipe you should realy just choose one if the enemy team has more single target lockdown abilities BKB is the way to go while if there abilities are more AoE damage pipe would be the better choice. AC though is a generaly good choice for DK giving him a higher attack speed and reducing the enemies armor.
Heart would be a good pick up to give you some damage and general survivability. Satanic could also be a good choice to upgrade your helm to get more lifesteal and if used at the right time can give you two lives in a teamfight. Halberd could be could if the other team has a hard right clicking carry that you need more disables to shut down. While mjollnir will be good to add more AoE damage and attack speed mixed with even more pushing power
This hero would fit very well into a pushing or teamfight line up because of his ultimate and survivability. This hero is also very good against line ups with an agility carry because his level three ultimate reduces attack speed.
This hero is popular in the chinese and SEA scene but some NA and EU teams have experimented with him