Voiced and unvoiced consonants

hello I have some troubles to distinguish between the sounds of words like:

rice -- rise
ride ---- write
etc

as far as I know the only difference between both words are the voiced and unvoiced consonants, Do you know a tongue twister or an exercise to improve this stuff ?. The words in isolation are not a big problem with some effort I can appreciate the difference, the real problem is the words in a sentence and at a normal pace.