Pinning a post to your profile page to me is the single most important way to get retweets.
Why? Because when people go to your profile page, it gives them something to retweet. They don't have to make anything up and it shows their support.
Now to pin a tweet to your profile page-
1. Create a tweet and hit enter.
2. Find it in your stream and click on the ...(three dots in the corner of the post) Sometimes this is in the far right bottom corner, sometimes in the far left bottom corner. Click on it an a list of options will appear.
The one second from the bottom is Pin to Profile Page.
Click on that option and another screen will come up asking if you are sure you want to pin to your profile page.
Then at the top of the screen will come up a message asking if you want to view your page.
Click yes or refresh screen.
You will now see the tweet you created at the top of your profile page. From now on, it will stay at the top of your profile page until you change it.
The numbers under the post will tell you the number of people who have retweeted the post.
I personally, change this out often, but it is up to you how often you want to change your top post.
Hope this helps you get more tweets,