The phrase "I mainly did" is grammatically correct and can be used in written English.
For example, you could say, "I mainly did the work myself, but some of it was done with help from my colleagues."
I mainly did drawing and made things out of Plasticine.
When I started foraging here, I mainly did it for myself.
When I started out, I mainly did it for health reasons and to lose weight.
"I mainly did this to obtain wealth and become well-known," CCTV quoted Mr. Chen as saying.
I mainly did finishing with them, not much else, but I could see as well how professional they were and how they looked after themselves.
This morning during my meditation session – which, honestly, I mainly did because I knew I had to write this piece – my mind flitted from thumbprint cookies to a scrap of lyrics by the punk band Au Pairs to what I'm going to make for dinner to how awesome it would be to have an entire glacial crater lake full of mint chocolate chip ice cream.
I mainly do it with draping.
I mainly do events waitressing and bartending.
"I mainly do it because it's fun," he says.
"I mainly do it for the cakes," he answers.
"I was working on 'Snow Falling on Cedars' and driving back and forth to Vancouver because I mainly don't fly," said Mr. Shepard, who lives in Minneapolis.
