How to improve my pronunciation of Mandarin? (Beijing)

Hello everyone,

I have reached a certain level in Mandarin Chinese that allows me to understand some daily conversations between Chinese people.

This is good, since my family-in-law is Chinese.

The trouble is, most of the time, I find it very hard to make me understood by them. Even though I use correct words and syntax, they just don't get what I'm saying.

The problem is even worse with total strangers.

What tips, methods or tools would you recommend for me to improve my Chinese pronunciation?

Thanks in advance for your help!