It is important to know when to use
if and when to use
whether. That is not something that is easy to explain, but I will try. (Perhaps I will get some help.)
Re:
Think about if you can be a responsible pet owner.
The word
if does not work there. Instead, say "Think about
whether you can be a responsible pet owner. Or, say "Think about whether you can handle the responsibility of owning a pet. Or: "Think about whether you are up to owning a pet." Or you could say: "Before you get a pet decide if it is more responsibility than you can handle.
Re:
Consider if the pet you choose will suit your living space.
I think
whether is also better there. Instead, I would say: "Consider whether the pet you choose will suit your living space." Or: "Consider whether you have enough room."
Consult the definitions at Dictionary.com.
~R