Vera, a few points:
1. "I wish" is followed by "were" only if it is generally agreed that the wish is a dead certain impossibility. Thus "I wish I were David Beckham."
2. In other circumstances, follow normal subject-verb agreement. For example, "I wish he was more sensitive."
3. Regarding your additional question about shouting, "I wish he would stop shouting at me" technically means that the wish is for something to happen in the future, however near (in the next minute) or distant. "I wish he was not constantly shouting at me" is a wish for a miraculous change in the situation in which you now find yourself. To all intents and purposes, the two sentences mean the same thing, but in technical grammatical analysis, they are regarded as different.
4. Please note that "wish" necessitates the use of the subjunctive mood of the verb in the clause that follows: "was" is not the past tense; it is the verb to be in the subjunctive mood. Modern grammar teachers and books (including the BBC) think that by telling students "to use the past tense", they are making it easier. If fact they are just preventing students from learning properly. How did your teacher teach you "wish and the subjunctive mood"?
5. In your example, if you use "stop", you would have to use "would stop" and not "stop" because it would have to be an action in future. With some verbs, which describe an existing situation, you do not need the "would"; for example, "I wish I lived in Paris."