Nova is an offensive/utility Warframe that excels in speed running, quickly dispatching large numbers of enemies, and killing bosses. What she lacks in defensive abilities, she makes up for in pure offense.
As she has a polarity, consider using Corrosive Projection, as it will lower the enemy armor rating by 30%, allowing Molecular Prime to deal more damage to armored enemies. At high levels, it is ideal to use in place of energy siphon.
Null Star can be used for both offensive and defensive purposes. It is relatively unremarkable when unranked, but at max rank, it can prove to be quite useful.
For offensive purposes, it can deal a good amount of damage to a single target by itself, dealing a total of 1200 damage after all six particles have launched (or more, if you are using Continuity and Constitution). Keep in mind that each particle will stun on hit, allowing you to continually stagger a target while you attack them.
Defensively, it is wise to use it before reviving an ally or accessing a terminal, as you are very vulnerable when doing either. Activating Null Star beforehand can stun or kill any enemies nearby that decide to attack you, preventing you from taking a lot of unnecessary damage.
On higher enemy ranks Nova may wish to use the skill in the same manner as Rhino's Iron Skin and recast it every time it is depleted as this will prevent her from being blindsided by enemies that are stuck in corners or behind obstacles. This is particularly important in Grineer tilesets because infantry will often jam themselves into corners on either side of the round doorways and open fire as soon as the player passes by.
Undeniably one of the most powerful abilities in Warframe, Antimatter Drop's power does not lie in its base damage, but in absorbing damage. Antimatter Drop absorbs all incoming fire, increasing the damage it will deal upon detonation with each shot. At max rank, the absorbed damage will be multiplied by 4.
It is wise to have a full clip before releasing an Antimatter Drop. Upon using the ability, continue firing at it nonstop. A high powered fully modded, max ranked, potato'd weapon, especially ones that do a large amount of damage, such as the Flux Rifle, Acrid or Lanka, can easily cause Antimatter Drop to deal well over 20,000 damage, instantly killing almost any boss. Using weapons with 100% accuracy or small spreads allows Nova to continue pouring bullets into the Drop for a longer period of time.
Antimatter Drop can be tricky to control though, as it moves based on where you are facing, whether you are aiming or not. Keep this in mind to control it. If you aren't absolutely sure that enemy fire will kill you it may be wiser to persevere through the hail of bullets and continue guiding the Drop until it detonates as prematurely running for cover may cause a loaded drop to float back to you and waste your invested ammo.
Wormhole opens up a one-way portal that will teleport anyone that enters it, friend or foe, to the target location. This is useful for rushing missions, helping allies catch up, reaching otherwise difficult-to-reach areas, or messing with enemies (And some unsuspecting allies as well). Be sure to upgrade it, as this will increase the number of uses per Wormhole.
A devastating ability, it does no damage initially, but primes targets in the area. Primed targets are slowed by 30% and takes double damage. Upon death, a target will explode doing it's damage, often detonating other nearby primed targets. This allows for chain explosions; upgrading it will increase its damage greatly.
Molecular Prime works incredibly well in conjunction with Antimatter Drop, weakening a boss, or killing entire legions of enemies by triggering an explosion. A maxed Stretch is highly recommended with this ability.
It should be noted that the slow effect for Molecular Prime stacks with other abilities that slow. When used alongside Frost's Snowglobe, or other effects such as Cold elemental mods, this ability is also capable of bringing enemies and bosses to a grinding halt, dramatically slowing them and easing the capability of landing headshots for the whole team.