RewriteRule ^(.*)$ [newdomain.com...] [R=301,L]
This will tell any device that visits the old domain to look for the same page on the new domain instead.
I've recently done a domain move and it was horrible :( Rankings took 7 weeks to come back to 75% - we still aren't completely recovered.
If you have time on your side, I would suggest you move a part of the site at a time.
I think I will keep the old site as it is while changing the content to reflect our new business at the same time as optimizing the new URL.
I would rather have people see us under an old URL than not see us at all.
I wish there was a way to switch URL's without the drop in SERPs... but then I suppose I am not alone in this...
So here I go building a new site. Oh bother...