How to get synths to play nice with guitars?

I haven't experimented much with synths, but I have a bit with strings and stuff so I think its fairly similar. I find I get the best results when I scoop the strings/synths quite a lot, and use no compression, so that sometimes they get buried, sometimes they soar above the guitars. A nice dip in the mids, and then also at 3-5khz otherwise it gets boxy.