Here are resources/aids which help you read Gurbani correctly, usually taught by an Ustaad (Teacher):
Baal Updesh – 1st Pothee - The purpose of the first pothi is to learn the alphabet, correct sounds of individual letters and vowels (muharni) and increase your confidence in pronouncing harder words and sentences.
Audio Recording of Muharni (download from multimedia > audio):
Panjabi Primer - Learning Panjabi through English medium, please note this is merely an aid, not a substitue for not learning paath correctly.
Must Read: Respect of Gurbani -English Book, on what level of respect old sikhs and Guru’s themself gave to Guru Granth Sahib Ji, and what respect we should give.
Gurbani Paath Darpan - A more advanced Pothi, which contains correct pronunciations hints, pauses and explanations of Gurmat (The Guru’s Wisdom) (In Punjabi).
Mengeh Shabadhs Darpan – Correct paath for Mangeh (hard) shabadhs in Guru Granth Sahib Ji.
Here are Some Videos by Giaani Thakur Singh Ji, which help a learner on pronunciation and writing of Gurbani Letters. Very useful for beginners to improve their ability and fluency.