Ask HN: How to perform well in online coding test?

It seems that lot of companies hiring engineers are asking for online coding test now-a-days using sites such as hackerrank. It used to be white boarding sessions at onsite interview or may be that still happens.

I feel like I am kind of slow and like to take time to put enough thought in the process. I also tend to freeze when doing such tests. I don't know why.

I have written many complex programs in my career. E.g I wrote equivalent of Apache DataFu Hourglass algorithm for custom data processing requirement .

Can anyone elaborate tips and techniques for performing well in these online coding tests ?