It's quite simple actually, just do this :

1) Go to 'Edit HTML' under 'Design' in blogger and tick expand widget templates

2) Find (Ctrl + F) this line : <b:include data='blog' name='all-head-content'/>

3) Add this code right after it :

<meta content='DESCRIPTION HERE' name='description'/>
<meta content='KEYWORDS HERE' name='keywords'/>
<meta content='AUTHOR NAME HERE' name='author'/>

4) Change description with your blog description, keywords with your blog's keywords, author name with... you know.