わがままはもう言わない gets translated as "won't say anything selfish anymore." However, this doesn't really make sense. If I google "say anything selfish," what I find are sites that have translated わがままはもう言わない into English. It's not a phrase that is normally used in English and the phrase itself doesn't even seem to really make sense. I don't think that English speakers really understand what わがまま is since they always translate it directly into something that is grammatically correct but doesn't really make sense.
So what does わがままはもう言わない actually mean?
Can someone give some example sentences that exhibit わがまま?