All work and no play (makes Jack a dull boy).
If you take your work too seriously you won't have time to relax and have fun. You'll be a boring person if all you think about is work.
Many hands (make light work).
This is the opposite of "Too many cooks" and means that if we all work together we will complete the task more quickly than if we each work by ourselves.
A bad workman (always blames his tools).
If you don't do a task well it's because you don't have the skills to do it not because the instruments you used weren't good enough.
You can't teach an old dog (new tricks).
As people get older, they usually don't like to try new things or new ways of doing things.
Make hay (while the sun shines).
Don't wait till tomorrow to do what you can do today because tomorrow your circumstances might change and you may not be able to do it.