As you say, just follow the excellent example set for us by the Bereans:
These Jews were more receptive than those in Thessalonica, for they welcomed the message very eagerly and examined the scriptures every day to see whether these things were so.
Combined with John 16:13, there is no better way to safeguard yourself against error. The next best source for laying down a sure foundation is a recommended book that takes on any of the major cults, new or established.
And if that's still not enough for you, you can always complete the set with a 'standard' work on systematic theology. You wouldn't want to read it like a novel, but as a reference work that you will visit many times, you will find it invaluable.
Personally, I like Berkhof, but there are others to choose from if he's too heavy going for your taste. A primer might be a better choice for a recent convert.