have a goal
Best motivation for learning is that you need a goal to achieve something with your scripting. You need to have an idea about what you want to achieve. Then you will learn how effective the script can be and you can re-use what you wrote for other future tasks.
Do you want to automate a Windows application? AutoIt
Do you want to automate a manual command line job? Perl, ksh, sed, awk ...
Have a look the scripts/scripting sections at oreilly.com
Other possible languages for the above tasks are Java, C, C++, C# ...
free tools: vi, vim, Eclipse, Notepad++, SciTe
paid for tools: Komodo IDE, Microsoft Visual Studio, Dreamweaver
Platform? All of the above (scripts, tools) will run on most OSs: Linux, Unix, Windows, MacOS
howtoforge is a great place to start
but also consider: stackoverflow.com