Are You Able To Think In Any Musical Key?

To speak Spanish or German or French well, you have to be able to "think" in the language. It's the same with music...unless you can "think in Bb" when you're playing a song in the key of Bb, you will leave out flats, miss chords, etc. that are just not necessary to miss.

.....what each scale degree is

.....what the primary chords are

.....what the secondary chords are
.....what the fingering for the scale of that key is
.....what the relative minor key is
.....patterns that work particularly well in that key.

If you need help in this area, check out "How To Think In All 12 Keys"