Assalam o Alaikum,
These are the few general guidelines for correctly understanding and interpreting the teachings of Quran. These will never let you fall into the trap of any false belief or custom of any ignorant sunni and shia group, if you apply these rules and guidelines honestly.
1. Quran is the collection of Divine Speeches of Allah, which were revealed on different occasions, sometimes a single ayah was revealed, sometimes a group of two or more ayahs.
2. Quran is the primary source, hadith is the secondary source. Quran establishes the foundations of all beliefs and customs while hadith explain them.
3. Surahs in Quran are divided in groups based on their main subject and relation between their ayahs. There are total 7 such groups. Each group has one or more makki and madani surahs. For example in first group there are 1 makki (fatiha) and 4 madani surahs (from baqrah to maida). Same way count on the surahs as follows.
Group Makki surahs Madani surahs Main subject
1 1 4 Shariah
2 2 2 Risalah
3 14 1 Risalah
4 8 1 Tauheed
5 13 3 Tauheed
6 7 10 Akhirah
7 46 2 Akhirah
4. Within groups surahs of Quran are divided in pairs of two or three. Surahs in pair share the main subject, style and format of divine orders. One surah of pair explains half of subject and other surah of pair complete it. Like surah baqrah and surah al imran is a pair, surah nahl, surah isra and surah kahf is a pair, surah saf and surah juma is a pair, surah muzamil and surah mudasir is a pair, surah falaq and surah naas is a pair. Every surah is in pair with others.
5. There are two types of ayahs in Quran in general. As Allah said in Aal Imran 7.
He is the One Who has revealed to you the Book. Some of its verses are decisive - they are the foundation of the Book - while others are allegorical. Those whose hearts are infected with disbelief follow the allegorical part to mislead others and to give it their own interpretation, seeking for its hidden meanings, but no one knows its hidden meanings except Allah. Those who are well grounded in knowledge say: "We believe in it; it is all from our Rabb." None will take heed except the people of understanding.
6. Important concepts and words in Quran are repeated at least twice. So if at one place someone understood wrong then the other place will explain and clarify him. So try to find every concept in at least two different places in Quran (there can be more than two) for better understanding.
7. Whenever you single out any ayah of Quran and try to interpret it’s meaning, then first read it completely, and also 2 to 4 ayahs before and after the main ayah under study. This will help you to know the context of the subject and all other ayahs related to the subject.
8. First try to find the tafseer of any ayah from the Quran itself, due to the fact that concepts are repeated in Quran, don’t quickly jump to tafseer books. There are 6000+ ayahs in Quran, try to find from them first.
9. If you find two different beliefs or ahadith on any subject, first compare them with Quran. Anything that goes against the teachings of Quran must be rejected, as I said foundation of all beliefs and customs are in Quran, you just have to find them.
10. Many scholars say Quran is not easy to understand alone. You must have to refer other books as well. That concept is partially wrong. As it is said in Al Imran ayah 7 that there are two types of ayahs in Quran, similarly there are two perspectives of understanding the Quran. First is the basic guidance or remembrance (Tazakkur e Quran), from this perspective Quran is the easiest book ever. Anyone can get guidance from Quran alone without referring any other book. As Allah said in Surah Qamar four times ayah 17, 22, 32, 40 that “And We have certainly made the Qur'an easy for remembrance (Al-Zikr), so is there any who will remember?”. Other is deep thinking (Taddabur e Quran) about the consequences of events and affairs mentioned in Quran. From this perspective Quran is difficult, because not everyone can do this, only experts can.
For example, lets apply these rules to one of the most important concept in Quran which is mostly misunderstood by many shias and sunnis, i.e concept of waseela.
Word waseela is used two times in Quran. Surah Maida 35 and Surah Isra 57.
Maida 35 says… Seek waseela or means of nearness to Allah. (mostly this part of ayah is only quoted)
يَا أَيُّهَا الَّذِينَ آمَنُوا اتَّقُوا اللَّهَ وَابْتَغُوا إِلَيْهِ الْوَسِيلَةَ وَجَاهِدُوا فِي سَبِيلِهِ لَعَلَّكُمْ تُفْلِحُونَ
O believers! Fear Allah and seek the means to be closer to Him and make Jihad (struggle) in His Way so that you may be successful.
Isra 57 says… Those whom they call upon besides Allah, themselves seek waseela to Allah.
أُولَٰئِكَ الَّذِينَ يَدْعُونَ يَبْتَغُونَ إِلَىٰ رَبِّهِمُ الْوَسِيلَةَ أَيُّهُمْ أَقْرَبُ وَيَرْجُونَ رَحْمَتَهُ وَيَخَافُونَ عَذَابَهُ ۚ إِنَّ عَذَابَ رَبِّكَ كَانَ مَحْذُورًا
Those to whom they call, themselves seek the means of access to their Rabb - trying as to who can be more near - they hope for His Mercy and fear His punishment, for the punishment of your Rabb is terrible indeed.
There is no any third place in Quran where word waseela is used. So based on these two ayahs it is clear that calling upon others beside Allah in order to get closer to Allah is not the form of waseela mentioned in Maida 35. As it is also confirmed by Zumar 3.
أَلَا لِلَّهِ الدِّينُ الْخَالِصُ ۚ وَالَّذِينَ اتَّخَذُوا مِنْ دُونِهِ أَوْلِيَاءَ مَا نَعْبُدُهُمْ إِلَّا لِيُقَرِّبُونَا إِلَى اللَّهِ زُلْفَىٰ إِنَّ اللَّهَ يَحْكُمُ بَيْنَهُمْ فِي مَا هُمْ فِيهِ يَخْتَلِفُونَ ۗ إِنَّ اللَّهَ لَا يَهْدِي مَنْ هُوَ كَاذِبٌ كَفَّارٌ
He is the One Who has revealed to you the Book. Some of its verses are decisive - they are the foundation of the Book - while others are allegorical. Those whose hearts are infected with disbelief follow the allegorical part to mislead others and to give it their own interpretation, seeking for its hidden meanings, but no one knows its hidden meanings except Allah. Those who are well grounded in knowledge say: "We believe in it; it is all from our Rabb." None will take heed except the people of understanding.
TASK FOR SHIAS…
Now, same way apply these rules yourself to those ayahs which are the foundations of your beliefs just to confirm that whether they are in accordance with the teachings of Quran or against it. When you do this keep in mind “There is no value of personal feelings and desires in the field of knowledge”.
Here are some single ousted ayahs that are behind your (shia) major beliefs.
Surah Baqrah ayah 124 (About Imamat)
Surah Nisa ayah 59 (About Ulil Amr)
Surah Rad ayah 43 (About who is witness)
Surah Maida ayah 55 (About wilayat)
Surah Maida ayah 69 (About delivery of message)
Surah Nisa ayah 24-25 (About Mutah)
Surah Saad ayah 75 (About who are aaleen) etc
If anyone knows more such rules please inform me and others as well.
Jazak Allah khairan.