Set it pointing towards your planned flight path trajectory, your Flight Path Vector (FPV) can assist you in determining that angle, which changes throughout departure until in cruise.
On 737, +5 for departure looks nicely in the area you will be flying into, reducing to 0 or -2 into cruise...
During climb the FPV can be displayed on the NG, thus allowing you to routinely match the weather radar tilt angle to the actual angle achieved in the climb.
During descent, look at 0 to -2 until you find ground returns, then reduce scale to avoid clutter until the approach segment.
During the approach segment, point it back up to +5, ready to look at any weather in the path of a possible missed approach, or for the next departure...