This is a guide for the 7.5 meta build for my main champ: Lucian
Lucian has been a really weak pick for the past few patches, due to the dominance of assassins, tanks and long range poke-based marksmans such as Varus, Jhin, Caitlyn, Miss fortune and many others, but in this patch (7.5) thanks to some Buffs and many nerfs to these guys i mentioned before, it looks like my main (190k exp) is now viable again.
In particular, Lucian seems to be on a good spot thanks to a new build aimed to maximize the dmg from his passive.
The reason I'm writing this guide is that in almost every guide I read about this build I found several mistakes (for example overcapped CDR, or on the opposite side non enough CDR) so I wanted to share with the community my own way of building him in this patch.
IMPORTANT ADVICE: before talking about single aspects of this build, you have to be aware of the fact that this is a quite risky build, let me explain: this is a MID/LATE Game build, that gives you a huge powerspike in midgame and a decent lategame, but it's slightly weaker in early game rather than other build paths due to the fact that it's a VERY expensive build that won't unleash its potential until you have the 2 core items (BotRK and Tri-Force). I don't recommend this build if you feel like you can't get a lead during the laning phase (CS advantage or in the best scenario an early kill). having said that, let's go to the build.

AS quints helps you to farm better during the laning phase.
AD marsk for more trade potential in the early game.
Armor seals because as an ADC,9 times out of 10 you'll be matched against an AD-based champ.
Scaling CRD glyphs to reach the needed 40% CDR at level 18, that allows you to dash all around dodgin' skillshots and procing your passive.
Scaling MR glyphs to deal with AP threats.

For masteries I run a 18/0/12 with Fervor of battle as keystone, cause at the momen is by far the best keystone you can use with Lucian, in fact I belive he's probably the best users of this mastery among marksman, because you can reach max stacks in a really short time due to his passive.

Blade of the Ruined Kings is a good first item cause it gives Lucian AD, AS and lifesteal, giving you a nice trade potential due to the sustain it provides, even if you won't have the same burst dmg of a Ghostblade or an Essence Reaver.
The BotRK's % health dmg will give its best in late game, especially against health stacking tanks, but it's also pretty effective against squishy targets.
I usually purchase tier 1 boots at the first back for the movement speed to go back in lane earlier and to dodge skillshots, before completing the BotRK, and I upgrade them to Ioninan Boots while building the Tri-Force.
Now we've reached the most dangerous part of the game: Building the Tri-Force.
This is a very expensive item, and it won't give you a relevant increase of dmg until it's completed.
this item biggest contribute to your kit is the sheen passive, because the 200% base AD bonus dmg after using an ability has a very good synergy with Lucian's passive, 'cause if you're playing him correctly you ALWAYS want to use your autos after an ability. it also gives you 20% CDR that combined with Ionian and runes allows you to reach 40% CDR, and finally spam your dashes and become a kiting god.
The second part of this build is a standard ADC crit build, aimed to maximize your DPS in late game.
I usually build Phantom Dancer before Infinity Edge 'cause I like the smooth feel that the PD's bonus AS gives you while performing your combos. This items also provides a dmg reduction while fighting an enemy champ, making you a stronger duelist.
With Infinity Edge you hit the 50% crit chance, and with the increased crit dmg that I.E.'s passive provides, you can now deal a huge burst with your base combo (AA,Q,AA,E,AA can literally shot a squishy carry).
Lord Dominik Regards is a pretty standard item to deal with tanks. Consider Mortal Reminder as an alternative in case the enemy team has someone like Mundo, Vladimir Nasus or a lifesteal-oriented ADC to reduce their healing.

That's all guys, this is my first guide, and I hope someone find this guide useful.
I apologize for eventual language errors, but English is not my mother language.
If you enjoy this guide let me now in the comments!