Let's get right down to it, Nova is pretty much one of the most OP hero right now, she is able to shut down almost any character except for high hp tanks such as Diablo and ETC. I'll first explain how this build works and why I picked each talents.

Nova was the supposed hero of Starcraft: Ghost that never happened. As a ghost, your job is to do recon work, find where the enemies are. Nova is not a laner, she can hold a lane, but she shines when she can go from lane to lane, poking, instilling fear into the enemy, and finding weakness, such as an enemy trying to jungle with low HP and you show up.

So the reason why she is OP is because of her 5th and 6th talents. The fifth talent enables to deal 25% of Nova's damage when she uses her ability. The clone ALWAYS uses Snipe > AA > Pin Shot > AA, and when she deals 25% damage, those abilities also do their effects. The 6th talent gives pinshot a 25% damage vulnerability, and this works on the clone too, and they STACK. So you can effectively drop your clone from long range (due to 2nd talent), and triple tap and it will deal more damage thanks to your clone, resetting its CD.

Talent #1
We pick Psi-Op Rangefinder for 2 reasons, it's a lot easy to shot stragglers and to get those tight kills. The second reason is for the 2 seconds cd reduction, with the base CD being 8 seconds, this is an effective 25% damage increase just from snipe. Some people prefer Ambush Snipe, I do not agree with that. It's good when solo ganking other assassins and supports, but when it comes to team fights, nothing beats the range and cd reduction.

Talent #2
Remote Delivery is my talent of choice here because I play Nova as a recon/clone ganker. The doubled ranged is insanely useful for vision, in a lot of map you can just drop a clone on a jungle camp to see if they are doing anything. Once you get the clone damage talent, this is even more useful because you can place it far ahead to break the mount of runners AND get a slow on them because of Pin shot. On top of that, the reduced CD means you can her more often, and everytime you do, the clone's Snipe/Pin shot are off the CD, a lot more damage. Gathering Power is a decent alternative if you can go 5 kills without dying often.

Talent #3
One in the Chamber is a no brainer here for 2 reasons. With your reduced CDs, it will proc a lot more often. Don't hesitate to spam your abilities and forgo one or two procs of it, but once the fights start rolling, you'll be using abilities on CD and using this non-stop. The alternatives are simply not attractive.

Talent #4
Triple Tap, again, a no brainer. Some people like to use Precision Strike, but it's too easy to dodge with most class. Once you hit level 20, the reset on kill is simply too powerful.

Talent #5
Lethal Decoy, the entire point of this build is around this. There is no alternative here, and I've already glorified the power of this talent.

Talent #6
Crippling Shot, again, no alternatives, the 25% damage increase is insane for team fights, it turns really hard tanks like Diablo into nothing, basically.

Talent #7
Fast Reload, no real alternatives here either. You can one shot someone by dropping a clone next to them then triple-tapping, the clone will have used pin-shot before the first hit of triple tap lands, and you'll generally one shot them. This works very well on ranged assassins like enemy novas, Valla, Falstad. In team fight, if you do a full opener combo (Clone > Pinshot > Snipe > AA) and follow by a Triple Tap, it's a guaranteed kill.