I can block on any hard start sounds but one thing some speech therapists say is a soft start technique. Say a soft H sound under your breath just to get air flowing and run it into the word you are trying to say. With some practice it's barely noticeable to the other person. It's hard to describe properly but if you are trying to say "today" then say hhhhhtoday. If I know I'm Gonna block on a word(sometimes you just know and it's a self causing problem) I find I can get out of it buy adding another word at the start which I guess does the same thing as the soft start technique. If I need to say "today I need to do XYZ" and I felt like I was definitely gonna block on today I'd say something like "well today I have to do XYZ." I hope this helps.