<meta name="keywords" content="BIT, thiết kế website hiệu quả, marketing online, thiết kế thương hiệu, cho thuê chỗ đặt máy chủ, seo website" />
I suspect that your keywords may not be ranked well because:
BIT (the site name and keyword) is not particularly meaningful).
Some key words are in English, others in Vietnamese, and some in a mixture. I'm not sure whether the search bots can cope with that.
The Vietnamese key phrases are each 4 to 6 words long. How many users will input search criteria matching them??? Key phrases are normally 1 to 3 words.
General comments: I think the site is over-designed. The backgrounds are visually stunning, but the constant switching between them is gross. I can't imagine staying on the site for more than 30 seconds. It is that annoying.