Do you wish to pronounce the Spanish /r/?

The way I see it, if you place the tip of your tongue at the very same point where you place it to pronounce the English /t/ of "tent" you will have won half the battle.
Let the tip of the tongue rest there. Now let air flow over it... it will trill. Practice pushing air over the tongue to force it to move and vibrate. The tongue will reverberate several times... and there you have the Spanish /r/.
After having tracticed this trilling for a while, you should try to tackle words with this sound. Practice makes perfect, and do not get into the actual words unless you command the vibration.
Then practice: perro, porro, rato, Rita, arroba, rorro, rana... go whole hog and exagerate the sound.
The soft sound of the /r/ you achieve by letting the tongue vibrate only once: hermano, artista, oro, loro, arte...
Then practice both: morro, moro / foro, forro / coro, corro / jara, jarra / caro / carro

Remember that my PHONÉTICA INGLESA compares both languages, the sounds of English and Spanish.