MontrealLady
well, it's just because i get disappointed when I do practice questions, and I get half of them wrong!!
i did a gmatprep last month and i got 430
i know that because my score is low, so its easy to improve it...but im soo bored and cannot concentrate any more

Well, that's easy to answer:
You are your worst enemy here. Real life (aspects of work, studying, etc) is BORING.
You say it's easy to improve, but then you follow up by saying you can't concentrate and are "soo bored".
You probably want to be at an 80%+ strike rate on some of the prep you do (depending on the difficulty of the question banks you're using). You have to keep in mind getting harder problems wrong on the GMAT affects you less than getting easy problems wrong. A streak of incorrect problems can also tank your score.
Final advice: Don't look for the ideal "strike" rate on getting problems correct. Focus on making sure you have solid grounding in the content, and getting through problems in the appropriate amount of time (average time overall, not time per individual problem).