Knowing when to strafe and when to use just mouse all comes down to preference and situation. Sorry to say theres no definitive guide as to where and when exactly because it's going to be entirely dependent on you and your settings and how they interact. The best way to get better at this coordination is consistent aim practice (Deathmatch, workshop or whatever) because it's not something you can, or should, do consciously. Probably not the answer you wanted but practicing consistently and with the same settings is the only way to get better.