I always suggest that people do an A/B on their first extraction.
This gives you a basic idea of what is going on, and is genearlly accepted as the correct way to extract alkaloids (although not always).
Check out our wiki page for different extractions.
My best advice is use less naphtha! If you are going for a freeze precipitation, use 100-200mL naphtha per solvent pull! Some teks say 400-500mL don't do it! You'll wonder why you didn't get much spice...and then you'll post here, and then we'll say to evaporate 1/2 of it...so use less!
Also a neat trick I leared. Once you pull off your 200mL naphtha and stick it in the freezer, put another 200mL into your extraction jug. Let that sit overnight while your are freeze precipitating the frist pull. Then switch. Put the naphtha that was in the jug int he freezer, and the naphtha that was in the freezer, (decant and save xtals) put into the jug. This way you always have something in the freezer and something in your jug.