七月三号二零一一年 二零一一年七月二日( our chinese always say something general at first and then say something detailed, such as we say, 我来自美国加利福尼亚洲instead of 我来自加利福尼亚美国；we say 二零一一年年七月二日instead of 七月二日二零一一年. and so on, just different from English right? do remember this~)

我刚被提升为和 （ I am not sure what do you exactly what to express here, because 提升 means improvement or promotion, do you mean you have got an promotion?  if so, congratulations and the right expression here is 我刚刚被提升为**（your position) )这个周末是七月四号---(  you'd better add a dash here for more explanation )我们的独立日。这个周末将是太神奇了  这必将是个妙不可言的周末！（we always use "了”at the end of a sentence to express something has been done. such as , 我吃饭了。 means I have already had my meal. But here the you haven,t arrive at the time, so you can not use"了”here.)
我们会放鞭炮，在饭馆吃饭，跳舞，和喝酒。我们将在（will）周末开个派对。我请客！干杯！

Here words in green are some corrections I made to make your sentence sound better and words in yellow are the reasons why I correct like these. And it's a diary isn't it? I'd like to say that in a very formal diary, besides the date, we will also wirte the whether at the top :)

In addition, I'd like to introduce a very useful chinese idiom here( the words in red) 妙不可言 which means something is is so wonderful and fascinating and I think it,s the meaning you want to express there~ By 神奇， we always use it to describe something magical, mystical and unbelievable.

Hope my words could help you~另外， 独立日快乐 ：）

best~

七月三号二零一一年(在表达时间方面，中国人永远按照年，月，日的顺序表达。所以，正确的表达方法是“二零一一年七月三号”。你的表达方式是典型的西方人对时间表达的习惯。)

我刚被提升为（这里缺少职位内容，没有这个内容，句子是不完整的。）和（虽然“和”也表示并列关系，但用“并且”更为合适——它也表达并列关系，而且体现发言者主观对内容的强调。）这个周末是七月四号（此处需要添加“，”）我们的独立日。这个周末将是（此处省略“将是”以保证句子的地道表达。中文不需要特定的词来表达时态（英语中用“will”能体现是语态是将来时，），而中文根据文章内容来判断时态。）太神奇了！
我们会放鞭炮，在饭馆吃饭，跳舞，和喝酒。我们周末开个派对。我请客！干杯！

PS：独立日快乐。你们的独立日，相当与中国的10月1日。中国人把10月1日称为“国庆节”——是庆祝国家成立的节日。

七月三号二零一一年

我刚被提升为和这个周末是七月四号，我们的独立日。这个周末将是（会）太（很）神奇了！
我们会放鞭炮，在饭馆吃饭，跳舞，和喝酒。我们（打算）（计划）（要在）（会在）周末开个派对。我请客！干杯！