Read this guide on how to use AMD WattMan utility (already installed on your PC inside the AMD driver suite).
For monitoring, WattMan has a stat graph at the top, but I like to use
GPUz
With AMD Polaris GPUs (like yours), overclocking is all about staying away from the power limit. Power limit throttling will generally kick in around...1250mV or so. If you need/want to go higher than that, you'll need to increase the "power limit %" to allow higher voltages. Simply sticking to "Auto" voltages will see you run into power limits almost immediately. Setting manual voltages (AMD WattMan is the best for this) allows you to keep voltages as low as possible while still being stable (which also keeps heat/noise to a minimum) and gives you more frequency headroom.
Each chip is different ("silicon lottery") but you could try and shoot for 1400MHz @ ~1150mV core clock. Sounds like around 1500MHz is about the limit (with more voltage of course)