I am currently writing a paper for a conference and i wanted to know the general guidelines for writing acknowledgements. The rule is to acknowledge the grant body and colleagues who have provided assistance or criticism.

My question here is, I have a friend who helped me in generating a graph which is used in the paper. I had been struggling with it for few days and my friend was able to generate the graph using a different software. It was quite simple but really important. I would like to acknowledge this help. But, I am not sure how to do so, and if it is normal since there is no direct contribution. Any advice?