Before I could roll my Rs I inserted "dr" sounds into the words instead. A quick, sharp "duh" (it should sound very similar to "tuh") puts your tongue in the right place. Then try saying "uh duh uh ruh uh duh uh ruh" very quickly while keeping your tongue forward.

Your "ruh" sounds should sound more like you're rolling them with practice. Also, keep in mind that you can roll your Rs without engaging your vocal cords - breath out strongly while keeping the tongue up at the roof of your mouth, and the tongue should flutter like a piece of paper.

If you can roll your Rs by themselves (just sitting there going "RRRRrrrrrrrr"...), then you're in luck (some people just can't do that). If you can, you should always try. I find that thinking of the Rs as being more forward in my mouth and on the tip of my tongue helps, as well as opening my mouth more in general. If you can't do it at all, I suppose you can keep trying, but you might be doomed. Be sure to try even more to distinguish between words that would sound the same otherwise ("Carro" (with rolled r) = car , "caro" (without it) = expensive; "perro" (with) = dog, "pero" (without) = but)

Try making the "r"sound while keeping your tongue against the roof of your mouth, this should make it vibrate and give you the rolled "r". Remember an 'r' at the neginning of a word is rolled as well e.g."rojo"

Keep in mind that the rolled "R" is almost a completely different sound from the soft variety. Don't try to modify the way you say the soft R to get to a rolled R. Instead, try slowly moving your tongue between the position you use to make the R sound and the one for the L sound (the D sound works too) while breathing out with a "sighing" action. If you do it right, your tongue should catch at some point and start making the correct sound.

There are some GREAT videos on Youtube - for 30 years as a Spanish student I couldn't do it but I now know how. Just search "Spanish trill".