Generally, unless you’re in a long term rental situation and you want to modify the space to fit your own personal preferences, home improvements should be done by the homeowner.
Now if by chance, you’re quite handy and the landlord would like you to do some fix ups, make sure everything you are about to undertake is documented in writing. Sit down with the landlord and go over the cost of the materials for the project and the expected time to actually do it. You should either be reimbursed for these items or the amount that you come up with should be deducted from your monthly rent. Consider yourself a part-time hire, and draw up a contract you both sign. This way you are protected should the landlord go back on the terms of your agreement!
In addition, should you be one of those people that just wants to make the space their own, make sure you okay any renovations with the landlord first. You don’t want to complete a project just to find out that you have to revert it back to the original design! For example, you wouldn’t want to install a new modern vessel sink, only to find that the landlord hates modern styles and wants their traditional bathroom back!