should i PAY more attention to grammar when i am speaking... it depends, if u talk to the foreigners, it will be not necessarily important. but if you teach the students in the class, it must be accurate.

As Charlie said, the expression is "pay attention to grammar". Perhaps you've confused it with "take care with my grammar". Well, the main thing is that the listener will try to understand you anyway. However, don't make the poor listener interpret every single sentence you say! If you continue talking with messy grammar, you will literally give the poor person a headache. Good grammar will solve the problem. So really, pay attention to what comes out of your mouth. Speak a little more slowly if need be. It will save you a lot of confusion and trouble... and people will take you seriously if you are earnestly trying, so don't be afraid of mistakes. As for the past perfect and present perfect tenses (there's also future perfect, did you know?), yes you should learn how to use them properly. Your meaning will become much clearer and you won't need to use so many simple sentences to explain yourself. Basically, when you use perfect tenses, you are using an earlier action to explain/describe a later situation. This way, you don't need to jump between timeframes (which is actually clumsy and wrong) and the listener will hear how certain actions are connected. Still, this is something you need to practise.