A quick 15-minute activity that gets you writing fluently online
Join a forum or chat of interest to you. There are forums for English learners where you can chat to other learners about learning English and about general topics. An example is at the link below.
You can also join a forum related to an interest you have, which is not necessarily for English learners. Here is a link to a site about fashion. Just search “fashion forum”, “football forum”, and so on.
Enter the forum for 15 minutes and write, either in one thread or in various. Your main objective is to write as much as you can in fifteen minutes. Write directly in the forum, without preparing. Remember, this exercise is to practise fluent writing.