Knowing the transfer window is the key. Check out Launch Window Planner for KSP. It tells you when to start your transfer down to the second. If you're within a

Knowing the transfer window is the key. Check out Launch Window Planner for KSP. It tells you when to start your transfer down to the second. If you're within a few minutes of that window, or even within a couple of days in that same section of the orbit, you'll get there fine with slight mid course correction. Now that KSP lets you plan your intercepts several sphere of influences away also makes planning easier. Just adjust your maneuver nodes until you see an intercept, then follow them.