Besides tha many issues that Magna Cartas has been added, this are 4 key beliefs that should have been added too.
1_ No taxes would be accepted before the previous debate and agreement of the chiefs and the most important merchants in town.
2_ Every chief and merchant who has accepted the new tax would have to sing a loyalty paper as an act of faith for his words and decisions.
3_ Every person will have the opportunity to be heard before going to a justice trial.
4_ No king could make battle decisions whitout a previous debate on the chief's court as regards battle issues and decisions.
This clauses will be added in order to make a more fair and respectful community in those times when Magna Carta was issued in 1215. Not only they will make sure that each person has the chance to be heard but also it will moderate the power of the king making him less powerful and givim more control to the people.