Dunno if this is the greatest method but this is what I do.
ISO
Coffee filters
Strainer
Square clear glass bowl
Razor blade
2x Glass/bowl or something bigger depending on amount of stuff your going to make oil from.
Hair dryer - optional for quick purging
Take your buds, put them in a glass, or bowl or whatever depending on amount of bud/shake/leaf/stem you have.
Pour ISO in to cover everything completely. Count to 12.
Pour out bud/iso mixture into your strainer over your second glass, bowl or whatever to filter the big chunks of crap out of the iso.
Clean strainer, put 2 coffee filters that are together into the strainer, then pour the semi filtered ISO into the coffee filter/strainer setup over your square clear glass bowl. Let ISO drain through filters. Takes some time depending on amount. Large amounts, pour slowly as coffee filter is slow.
Once the filtered ISO is now in your square clear glass bowl ... take a hair dryer and lightly blow dry the iso in the bowl until it is all gone. Do this in a well ventilated area, and hold a little distance from the bowl as sparks etc could ignite the off-gassing. If this method has you fearing explosions, then just leave the glass container out somewhere for 24-48 hours to purge/evap naturally.
A sticky semi movable clearish substance is left on the bottom of the bowl. Take razor blade, sterilize it if it's not, scrape the blade across the bottom of the bowl and watch the oil accumulate all over it. Again, depending on how much you make, you might need something bigger then a razor to scrape.
Take a dab, light it. If it catches on fire, chances are it isn't purged enough and you still have ISO in your oil.
Wait longer or hairdry more.
cheers