My method is to put my tongue flat on the roof of my mouth. The top of your mouth is curved, so I end up with the sides and tip of my tongue against the roof of my mouth, with the middle of my tongue not touching.
Open your mouth wide but almost closed (an English R will have your mouth in an O shape). It helps to pull back on the sides of your mouth. Remember, Chinese speak more inside their mouth with their mouth near closed. I teach them to open up their mouth more. So you need to close your mouth more.
With mouth barely open, and wide, fold the tip of your tongue down and pronounce an r.
The reason for holding the tip up, is because it will free you from using your mouth to hold the sound back before your pronunciation. We tend to use our mouths for that, and you need to have your mouth right.
With the tip down, you get a looseness in the r that approximates the Chinese R 99% perfect, without any effort.
If you find yourself still making an R sound, you didn't drop the tip of your tongue, or your moving your mouth into O shape.
To practice, put an English e in front. Er. Then after repetitions, shorten the emphasis on the e part, and you'll get a loose R as well.
I find the Chinese [ren (person)] to be the easiest to practice with.
To compare, the English R is pronounced by holding the sides of your tongue against the roof of your mouth with the tip already down, then holding your mouth in an O shape and pulling back on sides of mouth as your pronounce the letter. So, the exact opposite.