So much great advice! I'll throw in my two cents,
Building off another's advice of recording yourself, make sure to video record yourself, watch your mouth and compare it to the professionals you see on videos. Notice how much or how little their mouth is open when they are making certain notes. I had a terrible habit of yelping with my lips shaped like I was blowing out a candle. Till I forced myself to imitate grandpa and curl my lips over my teeth. The difference is night and day.
Keep practice sessions small to avoid bad habits, but when you do hit a yelp or cluck that's appealing to your ear, make that same note over and over to build muscle memory. Taking notice of how much tongue pressure you're using and the amount of air needed in your lungs to make the sound correctly.
Keep exposing yourself to instructional videos and like you did here keep asking for tips. Sooner or later someone will give you advice that clicks and you'll be over your hurdle.
And don't give up man! There's nothing more rewarding than talking a bird into doing something he wouldn't have otherwise done.