I am upper intermediate (stuck there forever…), but can converse somehow fluently. In the beginning, I was terrified by the tones, because the first time, I actually tried to speak someone Chinese, he didn’t understand what I wanted, just because I got the tones wrong. Unfortunately I never had the time and possibility to really drilling my tones, but they got better naturally after some time. So here are my suggestions:
1. Speak in sentences
When you speak in sentences, most Chinese can get the idea of what you are trying to say by the context, even when some tones are not correct. Also, there is also a melody to spoken sentences in natural speech. It sounds different, than if you would read a text character by character and would try to get every tone right.
2. Try shadowing and recording yourself
Listen a lot to natural Chinese speech and try to shadow, the way the people speak. Record yourself and compare the way the native speaker spoke and your way.