I usually use a negative tilt more than the pitch angle shown in the PFD during cruise (about 2.5 degrees up) so a tilt of -3 or more, depending on how far ahead you want to look, should work.

In ascent an even more negative tilt may be needed so you are not pointing the radar straight up into the upper atmosphere. In descent, a zero tilt, or even slight positive tilt if the PFD attitude bar is well below the horizon (in the brown), should work.

Also remember that, just because you see clouds it does not mean you will see radar returns. Radar senses precipitation (water droplets and hail) not fine cloud condensation, so you need to find an area of precipitation to see it working (as Markoz says, somewhere stormy with active thunderstorms or showers).

Rob