If you find that a particular sound is consistently giving you trouble, try revisiting how you pronounce that sound. When you get stuck on the 'h' in 'here', I bet the block happens way in the back of your throat, doesn't it (that's where my 'h's block). Instead of trying to make the 'h' sound way back there, move the sound closer to the front of your mouth, if that makes sense. Rather than trying to create the sound down in the back of your throat and then forcing it forward, try just letting the air flow out and don't create the sound until the air hits the very tip of your mouth. This general technique of 'moving sound creation to the front' instead of making sounds in the back of my throat and forcing them forward has helped me a lot over the years. It certainly takes time and lots of practice to essentially re-learn how to make certain sounds. But this method has proven very helpful for me.