We all like to be thought of as intelligent people.  One way to create this impression is to use "big words."  This is not a good idea in the job search process.  Remember, you are writing to busy people who want you to get to the point.  When you use long sentences with lots of big words, you slow them down.

Some experts on the subject suggest that "writing at an 8th grade level" is most appropriate.  Before you laugh consider this, the newspaper USA TODAY is written at that level.  You can measure the FOG FACTOR of your written documents if you use Microsoft Word.  Bill Atwood, an FOB Chapter Leader, supplies the following instructions:

Let the system do it.  You can configure your word processor to do this for you.   Here are the steps if you use Microsoft Word.  Other word processors would follow
similar procedures.

a. Select a passage in your document.  
b. Select Tools from the menu bar, then selecting Options in the
drop-down box. 
c. Select the Spelling & Grammar tab.
d. Select the "Show readability statistics" box.
e. Click "Check document."
f. In the Writing Style drop-down box, select "Standard".
g. Click OK.
h. On the tool bar click "Check spelling" 
i. Go through all the usual spell-check drill.

The results will be displayed in a "readability" window.