One really easy way that I often use:
cat "args" | xargs -P $NUM_PARALLEL command
ThisThe -P option for xargs will run the command, passing in each line of the "args" file, in parallel, running at most $NUM_PARALLEL$NUM_PARALLEL at the same time.
You can also look into the -I option for xargs-I option for xargs, if you need to substitute the input arguments in different places.