I have the same problem as most Asian Spanish learners with the Spanish single 'r' and 'l'. We usually mispronounce 'ala' as 'ara', and bra, bla. bre.ble .... etc are difficult for me to speak them accurately. So how should I pronounce single 'r' and 'l' correctly?
It actually depends on where the r is located in the word:
At the beginning after «l», «n», «s» or prefix «sub-» is pronounced as /r/
In other positions is pronounced as /ɾ/
l is always pronounced as /l/
You can check this pronunciation page to listen some samples.