Just battled a Rocket Grunt! 😃 It was at my mom's office building, which happens to be a Pokestop - I'd better tell her to stay safe, LOL.
I did pretty well, considering it was basically my first battle in GO; I mainly used an over-1000 CP Tauros. Failed at catching the Shadow Rattata, though :(
Managed to win every battle so far. Do recommend using Pokemon that resist attacks, as that can help a lot and you get more balls for catching the Shadow Pokemon based on how many survive in your side. Throw a ball after they attack as well (a second or so after) to minimise the chance of missing your throw due to it attacking mid-throw.
Only have bulbasaur and rattata so far... I want more variety!