registering to vote/switching utility/having a pet...
You have the right to register to vote, which can be done online rather than through an annual postal form.
If you pay the energy bills you have the right to switch provider and change the meter (though it is polite to let the landlord know this).
Your tenancy agreement might specify if you can get a pet and will normally require your landlord's permission - they should have a good reason to refuse.
Depending on how many people live in the property and where it is, your landlord may need to be licensed. If you feel like your landlord is being unreasonable, by banning overnight guests, for example, check if they need a licence and have one. Your council should have a public register of licensed homes to check* - let us know if yours doesn't.
Be aware that even if you have the legal right to do something, your landlord still has Section 21, the right to take back their property without needing a reason.
We are campaigning for the abolition of Section 21. Join us.
*Londoners can find a list of links here