Yep, obviously the centre point (the origin) needs to be dead centre of the model and then the model needs to be 0,0,0 in world space too.
One thing that really works for me is to use dynatopo in sculpt mode and then symmetrize your mesh that way. Then if you want you can use voxel remesher again if you prefer to work that way.
Just make sure the direction is correct when you hit symmetrize.
Hope that helps!