forget to do #
忘记要去做某事 Honey, why is the light still on? Sorry, I forgot to turn off the light before I left home.
forget doing #
忘记做过某事 I totally forget going shopping with you last week!
I was so drunk last night that I completely forgot talking to her at the party. I have no idea what I said to her.
Why is my phone in the bag? Maybe I forget putting it in there myself.
Examples #
Please remind me to take this book when I left here. I forgot to return it to the library yesterday.