I know there's some redundancy in this advice but I thought I'd mention it to support the great tips already here.
Practice. Read and write a lot of code. You might try to work your way through set problems like Project Euler or the Ruby Quiz or other competitions.
Learn the "laws of physics" of programming - some things are harder to do than others. all programming is an interplay between making a tiny, trivial and deterministic step on one hand and managing complexity through abstraction on the other.
it's most instructive to try things for yourself - even if you fail - but on the other hand make sure you attempt things you will definitely succeed at too because the feeling of success will fuel your passion. you will never be a great developer without passion!
Watch Douglas Crockford's JavaScript videos.
use Flanagan's Rhino book.
Try and use different programming patterns and styles in javascript: imperative, functional, object oriented, continuation-passing, dependency injection, fluent interface.
Always use var and semicolon.
Never use "with" or "eval".
Plan to learn another programming language (which smart people recommend you) and it will also greatly assist your javascript programming - you should not be too tied to a single language that you can't change. If you really like web 2.0 you should learn a good server side language as well. As a second to JavaScript for a youngster I would recommend Ruby or Python, (or PHP if you must). Other languages are really great for that purpose but these will be easier to learn first and will be readily available on cheap hosting providers. Those others may include: Lisp/Scheme, Smalltalk, Java, C#, Scala etc. Do not learn VB.
Get firebug.
Read "The Pragmatic Programmer".
Reuse code.
Write automated tests. You can use a unit test framework.
Write lots of cranky cryptic puzzle code right now. Get it out of your system. Then seek to write clean comprehensible code forever more.
Port code from another language.
Recognise that lots of people in professional development have absolutely no idea what they're talking about. Others are absolute genius gurus who's words you should memorise and meditate on. Good luck telling the difference!
Practice. Read and write a lot of code. You might try to work your way through set problems like Project Euler or the Ruby Quiz or other competitions.
Learn the "laws of physics" of programming - some things are harder to do than others. all programming is an interplay between making a tiny, trivial and deterministic step on one hand and managing complexity through abstraction on the other.
it's most instructive to try things for yourself - even if you fail - but on the other hand make sure you attempt things you will definitely succeed at too because the feeling of success will fuel your passion. you will never be a great developer without passion!
Watch Douglas Crockford's JavaScript videos.
use Flanagan's Rhino book.
Try and use different programming patterns and styles in javascript: imperative, functional, object oriented, continuation-passing, dependency injection, fluent interface.
Always use var and semicolon.
Never use "with" or "eval".
Plan to learn another programming language (which smart people recommend you) and it will also greatly assist your javascript programming - you should not be too tied to a single language that you can't change. If you really like web 2.0 you should learn a good server side language as well. As a second to JavaScript for a youngster I would recommend Ruby or Python, (or PHP if you must). Other languages are really great for that purpose but these will be easier to learn first and will be readily available on cheap hosting providers. Those others may include: Lisp/Scheme, Smalltalk, Java, C#, Scala etc. Do not learn VB.
Get firebug.
Read "The Pragmatic Programmer".
Reuse code.
Write automated tests. You can use a unit test framework.
Write lots of cranky cryptic puzzle code right now. Get it out of your system. Then seek to write clean comprehensible code forever more.
Port code from another language.
Recognise that lots of people in professional development have absolutely no idea what they're talking about. Others are absolute genius gurus who's words you should memorise and meditate on. Good luck telling the difference!
Use the force.