Tips on Shooting on Manual Mode

I would recommend you read something like Brian Petterson's Understanding Exposure. Manual mode only has three variables (aperture, ISO, and shutter speed), so it's not very complicated, but you do need to understand what each variable contributes to the final exposure. Different combinations of the three can center the needle for any given exposure, but creative decisions will dictate which combination to choose. That book does a good job of explaining these sorts of decisions.

 

Phrasikleia's recommendation is spot on. I have this book and am carefully studying it at present - a very useful read.

 

A book might help, but you'll learn best by experimenting with different settings. Then, examine the image differences and note the settings from the exif data.