Wordpress :-

Ok, with wordpress.com is quite hard to change Meta Tags, because they don't allow to edit their templates and also don't allow to use plugins.
but you can do following steps

1. Include a short description in the "tagline" field at settings > general.

2. Categorize and tag your posts appropriately with no more than a total of 10-12 tags + categories and you will do very well. WordPress.com has some of the best SEO there is.

3. Use keyword in your titles and in the bodies of your posts, but don't overdo it.

WordPress have a good SEO, so it can help you.

Blogspot

1. Go to your blogger Dashboard
2. Go to Design > Edit HTML
3. after and before tag add following code

In blogspot there is no any facility to add different Keywords and Discription for your different posts.
But you can do it mannualy

1]First Sign in to Blogger dashboard » Layout » Edit html
and find this line

2] Now, add the below code just below the above line

Replace “www.instantlymoney.com” with your particular blog post. please take a backup before using this code.

I hope it help you