We had flanking but ditched it. As mentioned above, It was too easy to get advantage and It really undermined the HELP action that is supposed to make combat more cinematic. The purpose of Advantage instead of static bonuses is to allow players to ask the GM, "hey, can I do this cool thing?" and the DM doesn't have to worry about saying, "no, there's no rules for that." Instead he says, "sure, narrate and I'll give someone advantage, or give your enemy disadvantage on their next attack"
One character uses HELP action to FLANK, allowing his ally advantage.
Or maybe he throws sand in an enemy's face, allowing his ally advantage.
Or maybe he screams an intimidating war-cry, allowing his ally advantage.
Maybe he swings from a chandelier and knocks the guy off balance, giving an enemy disadvantage.
It's way more exciting than having your players move their minis behind an enemy and say, 'I flank' all day long.
We are experimenting with using a bonus action instead of a full Help action and it's working pretty well. So to get advantage you can:
1) use a full action Help to give an ally advantage (as I suggested above) or;
2) move in to a flank position and use up your bonus action to give yourself advantage on your main action.
It forces you to use up a bonus action which has a lot of flexibility in 5e, depending on your build. So, maybe you give up an off-hand attack to get advantage. Or maybe you give up a quickened spell or a cunning action. And you still have to be in a flank position.