The first step to Bm is placing your index finger across the second fret of all the strings. It helps to have the top joint slightly hanging over the top. You want to press all the strings down, that way they all sound clear when plucked. Fine tune the index finger barre before moving onto the ring finger which goes on the fourth fret of the G string. Keep the top ring joint perpendicular that way you don’t touch the C string below it. This same barre shape is commonly used in other minor chords.