Could someone give three examples of how Shakespeare influenced the development of theatre?
1) Making language more colloquial. If you read the plays that come before Shakespeare (particularly Marlowe) and compare them to later Shakespeare plays, you'll discover that Shakespeare writes far more colloquially. In particular, Shakespeare adapts blank verse into a far more fluid and liquid form that doesn't sound unnatural in a character's mouth. To see what I mean, see below -
This is pre-Shakespearean verse:
O doleful day, unhappy hour, that loving child should see
His father dear before his face thus put to death should be!
And this is late Shakespeare:
Here's some flowers, and 'bout midnight, more.
The herbs that have on them cold dew o' the night
Are strewings fitt'st for graves.
2) The introduction of character. Harold Bloom, in particular, argues that this one is the case in his book "Shakespeare and the Invention of the Human". He thinks that Shakespeare, via fully-rounded characters like Falstaff and Rosaline (in, respectively "Henry IV" and "As You Like It"), was the first dramatist to really create believable humans, rather than stock character types.
3) New words. The words that Shakespeare invented - made up totally afresh for the first time - include assassination, sea-change, manager, director... and about 10,000 more. He is one of the most significant expanders of the English language by adding to its word-stock.