how can i improve my photoshop skills .?

Yes, to learn photoshop tutorials are a good resource. But keep in mind, Photoshop is just your toolbox, you'll still need your head/creativity to create cool stuff.

But also basic creativity can be "learned" somehow, because design follows rules that can be learned. Keep particing, go with open eyes through your life and think about how other solved design issues. Start watching creative blogs, look at advertisements and play around.

First: See tutorials, it can be text or video, just see and be inspired. TutsPlus is a good one.
Second: See everything to be inspired; You will need to combine those inspiration to create a new one, an original one, for your next project. Nothing in the world is fully original.

Repeat the first step until you are good.

Hey,
i think YouTube Tutorials are very great to learn. When i need something to know about Photoshop, i make it also with YouTUbe Tutorials.

Veja tutoriais no youtube, a melhor maneira de voc upar suas skills em designer

I do not know for sure, but I think brush helps a lot in photoshop

Does anybody use paint.net? How is it compared to photoshop?

Just follow along with tutorials on you-tube .....................

The easiest way to learn is to just get in there and do something with it. I used to watch tutorials on a particular area, for example, i didn't know anything about masks or layers so i watched a few videos and then applied what i learnt with some images i had.

I found there are some decent paid but if you dont have the money to fork out for paid tutorials there is a number of blogs and websites -- im sure even a few artists local to you - that will have some material teaching you how to do different things for free.

Just watch tutorials in youtube, keep practicing and you will be pro soon.

Just choose some topic that you have interest, like Creative Retouch, High-End Retouch, Concept Art, UI Design, Package Design... there is a lot to do, but if you try to get a piece of everything in a short time you probably will become overwhelmed. Check Behance, Artstation and Dribble and find what inspire you.