Best use of certification points in Planetside 2? [closed]

It depends on your playstyle.

Essential upgrades are:

• S-AMS for the Sunderer: 50 Certs
• Nanoweave or Flak for all classes: 1 cert for the first level, basically free

Recommended for organized play:

• Anti-Tank Mines for the Engineer: 100 Certs for level 1
• Scout Radar for the Flash: 50+100 Certs for the first 2 levels
• Anti-Air Lock-on launcher for the Heavy Assault: 725 Certs/700 SC (Alternatively Annihilator)
• Burster arm for the MAX: 1000 Certs/700 SC
• Skyguard for the Lightning: 1000 Certs/700 SC
• Mineguard for the Sunderer: 30+50 Certs for the first 2 levels
• Squad leader/Spawn beacon: 30 Certs
• Squad leader/Command channel: 100 Certs

Playstyle dependant:

• Rocket-Pods for ESF (Mosquito/Reaver/Scythe): 1000 Certs/700 SC
• HE or HEAT for the Lightning: 750 Certs/700 SC HE, 250 Certs/500 SC HEAT

In general, don't worry about wasting Certs. There is an infinite amount of Certs, so you will eventually unlock everything. Just try around, use the VR training area to trial stuff and if you unlock something and it turns out to be not your thing it's no big deal.