Okay, this advice isn't very common but it worked for me. I used to find it difficult to say words starting with G. I couldn't even say 'good morning'. So guess what, I started to say 'good morning' loudly again and again and again at my home and in about a week I could say it without any problems. These days I'm practicing words like tesla, tangent, and other words with T. It worked for me, you should try it too.