Robots
Just grab the robots.txt from presta site here and upload it to your root folder.
Open graph
For Presta 1.5 and 1.6 install the plugin found here.
For Presta 1.7 install the plugin found here.
Twitter card
Install the plugin found here.
Use CCC (Combine, Compress and Cache)
Go to Advanced Parameters > Performance and tick all in CCC section.
Redirect to https and www
# Canonical https/www
<IfModule mod_rewrite.c>
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} ^(.*)$ [NC]
RewriteRule (.*) https://www.example.com/$1 [R=301,L]
</IfModule>