well use a bit of common sense to rule out some. if you know what magick is, you can weed out some non-working spells that way [magick can't make us fly for example. any spell that claims they can won't work]
if you're short on time, perhaps try chants, or spells with few items. do a casting and wait a few weeks to observe any results.
if there's a particular spell that interests you but for whatever reason you can't cast it yourself, you could ask if others have cast it and what results they got.