Watch the Dorian online guitar lesson by Chris Buono from Modes That Matter
When it comes to improvising over changes there's two ways you can approach how to play over them--horizontally and/or vertically. The first approach refers to playing one scale across all the changes while the latter refers to changing scales per change. Ask any experienced improviser and they'll admit it's always more relaxing to play over changes horizontally. Such is the case over this minor blues in Bm where B Dorian works well over the i-7, IV-7, V7 and concluding V7#9 chord. Though they're not all directly diatonic to B Dorian, the horizontal approach works well nonetheless. To make that so, some strategic playing on your part is required. For instance, when playing over both types of V chords that have an A# as a 3rd itís a good idea to, at first, aim for playing the 5th of B Dorian (F#) as a target note that lands on the downbeat of the change and then let it ring out. This way you don't risk any clashes when playing over both instances of the V chord. About that, try playing Dorian straight thru and you'll surprised at how well it works regardless of the differences.