I know we've had one or two hero guides since this board was made, but hopefully making one that can be used regularly will help to restore the board's activity.
That said, I'll be making posting my quick guide to 6.86 Luna.
In the last year or so, Luna has had some off-and-on appearances in professional matches. She's a strong carry with plenty of presence throughout the entire match. Considering that she's been buffed here and there for four patches in a row, there's a lot of potential behind the hero that is overlooked.
>Skill build
Skill build is simple. Max Q, then E. Every time. Don't take Glaives until your other two skills are maxed. Glaives get stronger as the game progresses, while the other two don't scale as well. It's important to max your Q first so that your ult can actually do some damage. It's more than enough to get a kill on a solo enemy, so don't reject that shit. Q and E can help with harassing and E will give you a great advantage while competing for CS in lane. Level ult when you can, of course
>Early game
Pick up a cheap stat item to help with surviving the laning stage and farming a little faster. Ring of Aquila and Drums are good options. I like to pick up a Morbid Mask right after, since Luna is pretty squishy early on, but hits pretty hard. Luna also has the highest base movement speed in the game, so you can usually wait a little while to get boots.
Once you've got a setup where you can farm efficiently, you'll want to get a Blink Dagger. TRUST me, very important item on Luna. Not only does she have a pitiful attack range for a ranged hero, but your disable's range isn't very great either and your ultimate affects an area around you (See: Earthshaker, Tidehunter, Shadow Fiend, Puck, etc.) It gives you a more reliable escape than Shadow Blade, fits with your abilities, and allows for you to blink between jungle camps to accelerate your farm.
>Mid game
BKB is usually a good item to at least consider. Dragon Lance is a good all-around choice to pick up early, as it has helpful stats, a well-needed attack speed boost, and can be disassembled into a Butterfly and BKB/SnY. Speaking of SnY, it's a fairly good item for Luna, although scrubs tend to prefer Manta, which is shit on most ranged heroes. Survivability. Maim. Increased movement speed. DPS. Not always ideal, especially if you plan on getting other items to help solve your kiting issue, but definitely an item to consider. Diffusal Blade is another cost-efficient stat item that has a lot of utility.
>Late game
Luna's item selection for late game is honestly pretty lacking. Build for the situation between Satanic, Butterfly, Skadi, AC, MKB, and the previously mentioned mid-game items. Take advantage of your physical DPS and tear through creep waves and rack up tower damage. There aren't too many heroes who can out-carry Luna, so it you've made it this far, congrats. Don't throw.
>Other things to consider
Luna's a very strong hard carry, unless you waste your gold and inventory slots on shit like Agh's and Shadow Blade (Silver Edge is an okay choice if the break is really needed).
Yes, Luna's a farm vacuum, but she's got strong presence throughout the game. Help your team. Push lanes. Gank. Teamfight.