Get the horn off your face if you've been using for leverage against your chops. Work on your breathing, then lip buzzing, lip buzz, fingering horn or knuckles on your other hand, then buzz mouthpiece. Start jogging, swimming or cycling to build up your wind away from the horn. I went through many teachers but the best advice I got was from a fr. horn orchestra director, to blow straight ahead so my air was focus straight through the mouthpiece, into the leadpipe, not up or down. I decided not to mess with my lips anymore, just to blow straight ahead (w/o mp) then gradually focus my lips to support the air and eventually get a buzz. If I focused the air up or down I started over. When I got the buzz down, I added the mp. If I could buzz mothpiece, remove it and air still went straight ahead, I added horn. After I got the habit set, attacks were consistent, moving between notes no longer scary. Hope this helps.