There is no definitive method of finding "good rules", however this is an attempt at a general guide.
For outer-totalistic rules, one of the most basic principles is a lack of B1 and B2. (B0 also tends to create strange explosions.) Both are guaranteed to make your rule explosive. B3 is also going to be a requirement, as it can be easily proven that without B0, B1 or B2, B3 is required for any patterns to escape their bounding boxes.
Aside from that, it is generally a matter of removing transitions if the rule is too explosive, and adding them if the rule isn't chaotic enough. It helps to get a feel for what each transition is like, for example S0 and S1 tend to have very strong effects and S4 tends to create very large still lives, in combination with other things.
These are often a lot more interesting than outer-totalistic rules.
Analogous to outer-totalistic rules, your transitions to avoid are B0, B1e, B1c and B2a. You will also require one or both of these: B3i B3a and one or both of these: B2c B2e for patterns to be able to escape their bounding box/diamond. Making isotropic non-totalistic rules can be difficult, however once you get a "feel" for it you will start to notice general trends in rule "characters", such as the typical behavior of rules with S1 and a lot of B2 transitions. It helps to start first with a well known "good" rule, but otherwise there isn't much else to say. It may also help to think up a spaceship, attempt to make it work and then go from their, adding/removing transitions as required.