Yes, writing a lot of (well documented) code and continually improving it is a great way to learn!

I am over using the parameters ($_,@_) because ... I thought they operate faster

My suggestion would be: don't worry about speed until it becomes an issue. Saving a few milliseconds execution time is only sometimes important, but a lot of the time code readability and maintainability is more important. When writing, one should of course take care not to brute-force everything (like for example knowing to use a hash instead of grepping over an array where appropriate, or not reading a second input file once for every line of the main input, like two recent posts here), but as they say, premature optimization is the root of all evil. If the execution speed of a program does become an issue, then one can profile the code and optimize the places where it's actually slow.

I am recent graduate and looking forward to get a job in the telecommunication

http://jobs.perl.org ;-)