When manually meshing a region, the element quality can suffer. Is there a tool to "jiggle" or smooth the nodes into a more ideal arrangement for a selection of elements?
Strand7 had such a feature and I found it really useful.
Edit: I found it under Mesh / Smooth... for anyone searching for this topic in the future.
The best advice is to play with geometry, splitting surfaces to guide the mesher to create correct mesh at the first time, don't let the job automaticaly to the mesher.
I ply a lot also with 2-D mesh transition using command MESH > EDITING > INTERACTIVE, see my blog: https://iberisa.wordpress.com/2015/05/17/2-d-trans
I was interfacing an old mesh with a new add-on mesh, so it got a little dirty. But the smoothing did the trick quite well. It still looks ugly, but the element quality is much better.