Here's how I like to get the buttonhole placement on a shirt just right, tips on sewing buttonholes and a tutorial link to how to sew on a button.
Shirt-making – The G. G. Files
A Sleeveless Granville Shirt
Sew Alongs and Tutorials
Diary of a Sewing Fanatic: Shirt Sewing Tips
Shirt Making 101 with TomKat Stitchery
Diary of a Sewing Fanatic: Shirt Sewing Tips
button – Blog
The Perfect Blouse: Make the Buttonholes - Threads
Sew Alongs and Tutorials
Sewing Glossary: How To Draft And Sew Button Bands The Shirtmaking
How to Sew a Bound Buttonhole
The Correct Position of Buttons and Buttonholes - Designer Stitch