Alright, first of all let me introduce you to the silicon lottery, where each card is different from other card depending on the quality of the silicon, to overclock your gpu you need to do somehow a long process to be able to say that you have an overclocked stable GPU, thats the brief introduction.
Just add to your knowledge that your gpu is a factory overclocked one and comes with GPU Boost 2.0, I'll explain both, basically when Nvidia launches a reference design it sets the base clocks for Core and Frequency (lets not talk voltage and BIOS, these are the extreme part and an error in this section might damage or brick your card), when gaming the frequency of the card is changed dynamically by the GPU Boost, it checks your card temperate, how much power it is drawing and decides to increase/decrease frequency on the core, so a card with 1000mhz base clock and 1150mhz boost can reach a frequency over 1200mhz with GPU Boost in good condition, example of frequency changes over time on a different gpu
Steps that I recommend you do is to know more about your gpu, check the specs (ill suppose you are using msi gaming series)
https://www.msi.com/Graphics-card/GTX-970-GAMING-4G.html#hero-overview
Note: you can use MSI Gaming app to overclock your gpu by clicking 1 button (OC mode), an easy small boost to the card.
To check what the max frequency your gpu is able to hit, install MSI Afterburner and run it, it has a stats window with all information you need, and then install a benchmark software like 3DMark and run it, after it is done check the Core clock curve and check what value your gpu was able to hit and how stable the curve is, you might be happy with gpu boost giving you a good boost in core clocks without a manual OC, also monitor temperature and power draw
