How can I perform an efficient meshing in my 2D project?

Here are some advises for your 2D project meshing:

Use the aided mesh (by default) in any case;
If necessary, adjust the mesh with manual mesh point and remove relaxations locally;
When using manual mesh, use linked mesh as much as possible (for a slot in a rotating machine for example to save time);
If the results are not satisfactory, use the adaptive solver to refine the areas needed.