A. We use by to say how we do something. We use by (followed by a noun or -ing) when we talk about what action we take to do something.
*He only avoided the children in the road by braking hard.
*She succeeded in memorising the text by concentration.
*You can improve your English by reading more.
*She made herself ill by not eating properly. Creo que este uso sería tu "a base de"
However if the noun is plural or there is a determiner before the noun (eg: a, the, this, that, my, her etc) we use a different preposition, not by.
*I ordered it by phone / I ordered it on the phone
*She arrived by car / She arrived in her new car
B. We say something is done by somebody/something (the passive)
*The programme was watched by millions of people.
*Have you ever been bitten by a dog?
*A play by Shakespeare
C. By also means next to/beside
*Come and sit by me (=next to me)
*Where's the light switch? By the door.
D. Note the following use of by...
*Clare's salary has just gone up from €1000 a month to €1100. So it has increased by €100 / by 10%.
*John and Roger had a race over 100 m. Rober won by about 5 metres.