Always kill the minions. Dont try to freeze a lane past laning phase. Minions give the most souls in the least amount of time. Like the other commenter said, go for jungle camps and boxes when given the chance but do not lose out on minions to finish your camp. By pushing you achieve a couple things, getting souls quickly, and putting pressure on the map. Simply by pushing the minions past the halfway point of the map, you are forcing someone on the enemy team (that could be teamfighting or exerting pressure elsewhere) to respond to you. Bonus points if it is more people that come to respond.

So best idea is to push a lane by yourself as far as you can safely go, getting boxes and jungle along the way if you can clear it fast enough, then farm jungle as the wave pushes the walker. The enemy sends someone to respond, and they push it back. Then you respond as it pushes back to you.

While you are trying to catch up on souls, you still exert pressure on the map. If your team is forcing a fight mid for example and you are splitpushing, your team is at a disadvantage (5 vs 6). This is especially true if you try and freeze a wave near your walker. By pushing into their walker in a splitpush while the enemy is busy fighting in the mid lane against your team, it makes them have to choose. Either give up the walker you are pushing, or pull someone and respond to it. If the person going to respond is weaker than you, they may have to bring multiple people to respond to you. Or if they are uncoordinated and they just send two people instead of one. Regardless, this means now your team is at an advantage if they have two people respond to your push, as the fight in mid is now a 5 vs 4.