Make sure the graph is in its own tab. (When you create the graph, select the option, "Create in new tab," I think.)
Edit the graph as necessary. Here are the steps I take to get the best visual results: double click the bars (for a bar graph) or the lines (line graph) and select a heavier ("bolder") outline; change the colors as necessary; remove the lines going across the graphspace and any other useless marks; double click the X (horizontal) and Y (vertical) graph direction lines and select a heavier outline for those; bold all fonts and increase the font sizes (>20).
Hit Ctrl+A (this selects the entire graph).
Hit Ctrl+C to copy the entire graph.
Go to Photoshop (or Illustrator if you want to play around some more), select New image, click Yes or OK until you get to a canvas, and hit Ctrl+V immediately. The graph will look tiny but that's because it's zoomed out to 50% or 66% or whatever. So just zoom in if you want to see how things look up close.
This is your high-resolution copy. It should look bold and crisp. Save this as a PSD and as a JPEG to keep the high-resolution copy on file. Then resize the image, maybe to 50% its size or whatever, then save it as another name and it will change the file size concomitantly to make it more portable for documents and PowerPoint presentations.
Good luck... I tried to be as basic as possible in case the non-tech savvy could use this too.
Take care,
CG