Pickup choice can make a difference and their position. I like using multi band compression which can push the higher frequencies when needed but leave lower frequencies alone. EQ, of course, that will be useful - and a bit of drive. More saturation for a pronounced effect. If you want to make the harmonics stand out longer, then HPF a delay pedal so it only delays your high frequencies! But don't overdo it!
You can pluck harder towards the bridge, meaning a louder harmonic without the string flapping around too much. On some instruments I have found that plucking with my nail or a plectrum helps, but generally an accurate and good left hand technique is where it is at. I can get more volume out of any bass with good technique first without the addition of the above, but it does help