Hello dren1975 and welcome to the Forums!
 
Each graphics card is going to be different in how much of a clock offset you can apply. Below is a nice guide on overclocking using Precision XOC. You will have to play around with your card and see what feels comfortable and stable. Be careful as overclocking can always be a little risky.
 
http://www.babeltechreviews.com/overclocking-gtx-1080-precision-xoc/view-all/

For any card i usually start at +25 core and +50mem and go up in those increments after it passes. After it fails i lower both by -25 and leave core clock and up memory clock slowly +5/10. For gaming ill usually lower it by 50 for core clock and 100/200 for mem. Just personal perference