Use your frameline. You're pre-focused so you can forget about focusing and concentrate on what's happening in your viewfinder. Most people just use the frameline to frame but Leicas are nowhere near as good as SLRs in that department.
Street shooting is all about anticipation (yours). Try to select a distance from your main subject(s) that includes a fair amount of space outside the frameline for your lens. Think of that space as "off-stage" and the area inside the frameline as "on-stage". Pay attention to what's happening outside the frame and try to anticipate how what's happening there will impact the scene inside the frame a second or two later. That's how many of the greats capture their "decisive moments".
Using the framelines means a different way of thinking from using a DSLR or a mirrorless. It's what differentiates rangefinders from other bodies. Once you get the hang of it you never go back, at least for street shooting.