1:- Turn the writing direction "right to left" by pressing the right "Ctrl+Shift" where ever you want to write Urdu.
2:- Please chose any proper Urdu font like "Jameel Noori Nastaleeq". You can use any other Urdu font you like but the Nastaleeq font is often recommended because it's very common and very beautiful.
3:- The rules for giving "Space" in "Urdu" are much like the rules for English. As we do for English give a "Space" after each word and end your sentences with a "Khatma" (Urdu full stop) without any space between the last word and the "Khatma". If you start a new sentence in same paragraph, give a space before the first word of the sentence. The same rule is applied for the "Coma".
4:- Whenever you need to write "Yeh" in middle of any word, always write "Chooti Yeh" instead of "Bari yeh" likewise whenever you need to write "Noon" in middle of any word, always write "Noon" instead of "Noon Ghunna".
5:- If you want to type "Alif mad" then use one key instead of typing "Alif" first and then put a "Mad" on it. According to the Urdu Phonetic Keyboard, you can write "Alif mad" with "Shif+a".
6:- The lettre "Hamza" is frequently used while writing Urdu. In computer's Urdu it makes different shapes in the above, below, beginning, middle and end of word. While typing Urdu on computer, for every form of "Hamza" a different key is used. According to the Urdu Phonetic Keyboard, if you want to type "Hamza" in the middle of any word, you can type it by pressing "u" and to type "Hamza" at the end of a word press "Shift+u". The letter "Wao" with "Hamza" is placed at the single key like "Alif mad" so you can type it by pressing "Shift+w".
Note:- Try to write in a proper way, it makes not only your words valuable but also it is important for those who want to search through.
A complete map of Urdu Phonetic Keyboard layout is available here.