This introduction by Etter is crisp, clear and very well-presented with many helpful examples, that range from elementary (and useful) scripts to a thoughtful introduction to signal analysis (ch. 10) and control systems (ch. 11).
Another good book to consider is
F. Gustafsson and N. Bergman, Matlab for Engineers Explained:
This book includes elementary and advance topics in Matlab and 12 applications of Matlab. The applications section of this book is superior to the application chapters in Etter's book. Very helpful supplementary material (scripts) for this book are available at
http://users.isy.liu.se/en/rt/fredrik/
Another place to consider is the two-part lecture series on Matlab:
Engineering CEE 20: Engineering Problem Solving. Lecture 1. Introduction to MATLAB, Part I
https://www.youtube.com/watch?v=ZNID-t9UeFQ
Engineering CEE 20: Engineering Problem Solving. Lecture 2. Introduction to MATLAB. Part II
I think the best way to learn is using the built-in Matlab Help. You can pull information in two ways. First, you can go to the Help tab and look for what you need. The information is very clear to understand and usually every page contains useful examples. Also you can pull information directly from the command line using "help" plus the command you need. For example:
>>help plot
will bring information on the basic syntax to prepare graphs, etc.
Also you can find a great amount of scripts and useful functions in the Mathworks website.
If you are starting from scratch, my suggestion is to go to the Matlab Help and get familiar with the way Matlab operates through arrays and matrices, etc. Just follow the topics readily available for you. This is better than any book. Good luck!
It is better to promote and understand required principles of engineering field and then use MATLAB or other software. they are languages and you should run them.
I totally agree with M Cazorla - use the help. You will find "getting started" sections for basic Matlab functionality and every toolbox. In the latest releases these are even expanded by good examples. In many cases, this will also give you a direct solution to the problem you try to solve (there are MANY functions already built-in).
In addition, I would recommend the video tutorials in the Matlab Youtube-channel (see link). Finally, it is also of great help to have a Mathworks account and browse through Matlabcentral for specific questions (see link) or to try some of the challenges posted in Cody. With a Mathworks account you can also sign up for the Webinars which are most often targeted at a specific group of people.