i am way rusty with acm so keep that in mind, but the merge is the opening move between you and your opponent whereby you gain an advantage at the start and keep building on that advantage until you have guns solution on the bogie and shoot him down. when done correctly against a competent opponent, the time between the merge and you shooting him down can take minutes, so there's a lot more to it than just the merge.
also, there isn't a standard merge tactic that can be applied to every situation. you must know the opposing aircraft's strengths and weaknesses and how they stack up against yours, as well as their relative e state compare to yours. those factors dictate what merge tactic you use. sometimes, the best merge tactic is to keep going because the chips are stacked against you.
some examples are to perform a lead turn before the actual merge so you get started before your opponent. sometimes, you do an immelman to bleed speed to decrease your turn radius, or do a split s to gain speed to increase maneuverability. sometimes the merge is solely intended to get your opponent to bleed his speed so you can either outturn our outclimb him. other times, the merge is to get him to slow down so you have the acceleration and speed to get away.
basically, i'd say if you have a plane with better climb rate but slightly worse turn rate than your opponent, don't keep turning with him because he'll get you. instead, get him co-e then start a climbing spiral to get on top of him and bnz him to death. if the roles are reversed and you see him going for alt, you need to kill him fast or start thinking about leaving. if your plane climbs great but turns poorly, extend for alt and come back and bnz him.
i find the best way to practice merge tactics is in a training environment where you can eliminate as much variables as possible, and do so with an ideal setup. once you have it perfected, do the same thing against an opponent with more or less e than you so you'd know how well, or how poorly, that one tactic works in those situations. then keep changing things up until you find what works in which situation.