Declension is defined as the angular distance north or south of the celestial equator. As the declinations define a semi-circle from the south pole to the north pole, they cover a total of 180 . The celestial equator runs just north of the Belt of Orion, just south of Pisces and just north of Libra, right around the celestial globe. This is a difference of a little over 15.5 degrees. So you could describe Rigel as 10 west of Betelgeuse and 15.5 south.
Circumpolar constellations take a little more thought.
Looking at Ursa Major, you'll see that it too has its RA increasing right to left, from 8 hours to 14 hours. In the spring Ursa Major is high in the sky, upside down. The handle points eastward, and indeed its stars are properly arranged so things which appear east are actually to the east. When you see Ursa Major in the winter, low in the sky and right side up, it is actually reversed. In my Pocket Guide I describe M101 as 5.5 east of zeta.