I have found that especially for lighting circuits, there is no true "best way." This is because very often the installation
itself limits one's options, so it is best to "do as well as you can." Often, the first thing to go is the desire to properly secure the joint to avoid flexing, as there may be no room or access to do so. So, do what you can, and ignore the rest. Unless, of course, it is a "mission critical" installation
-- i.e. if the joint fails you might find yourself in serious do-do.
Assuming a butt connector is the most expedient solution,
1. Use good self-adhesive heat shrink connectors with a proper crimper.
2. If you have space (and you probably do) add a heat-shrink sleeve over the finished connector. This not only adds moisture resistance, it also adds strain-relief to the joint and helps avoids failures from flexing.
3. Secure the connection if you can. Often (at least for interior
work) the connection ends up being stuffed into an overhead where stuff really can't move much anyway.
While there may be a "perfect" way to do this, remember that perfection is often the enemy of progress.