"Please walk towards the left side."
This left side right side is confusing. Do you mean turn left? Theres a big difference between keeping left and turning left.
I think "请往左走" is enough if you want to say "please turn left".
"Please keep left" would be "请靠左走".
"Please walk towards the left side." is a literal translation of the Chinese sentence. I am however not sure if it's interchangeable with the first one or should you use it only when you mean you should go to left side of some place.
For example: 往街道的左边走。