These are my techniques:
Changing the order of the sentence:
I was happy because of what she did.
What she did made me happy.
Using "in" and "on":
1999 was the year I devoted myself fully to marine biology.
In 1999, I devoted myself fully to marine biology.
Inverting the order of the sentence:
Maybe it was my mistake.
My mistake, maybe.
I checked the newspapers on the wall. They were all about the crime.
I checked the newspapers on the wall. Newspapers about the crime. All of them.
Replacing "was" with a more "interesting" verb:
The hotel we booked was next to the river.
The hotel we booked sat next to the river.
Replacing "there wasn't/it wasn't" with "not":
There wasn't a single dress.
Not a single dress.
It wasn't that we didn't care about the house.
Not that we didn't care about the house.
Removing "it/he/she was":
We reached the hotel. It was a cozy place. I liked it.
We reached the hotel. A cozy place. I liked it.
A man approached my table. He was handsome, maybe in his thirties.
A man approached my table. Handsome, maybe in his thirties.
What do you think of these techniques? What are yours?