Check out gw2timer.com you can find out all the times of the meta events. Keep your lfg open around the time the meta starts and you’ll see squads pop up. Typically people just do meta events because they’re the most rewarding but if you want to do pre-events then you’ll have to look harder for a group. Just keep the lfg tool open in the corner of your screen. Also, if you do go into one of these maps during meta event you’ll likely be shoved into a less popular map as the heavily populated maps are capped out. So taxiing to a more populated map is crucial.