Your best bet is to search for material online.

Read news articles and see how they write every word. It's important to note when, for instance, ښ is used instead of خ, when ږ is used instead of ګ, when ځ is used instead of ز, when څ is used and so on.

Two resources that will help you in this are the Mashal Radio website and the online Pashto keyboard. That is how I learnt to write in the Pashto alphabet, which is very different from the Urdu version.