I think the single most important step you can take towards playing more consistently is to slow down and think, in every stage of the game, but especially the team preview stage.
Identifying threats is a crucial step to playing consistently for any style of team you use. If you're playing offensively, as it sounds like you are, noticing the potentially troublesome walls, and dangerous sweepers that can outspeed or threaten your sweepers can allow you to plan ahead, and have a course of action, as well as contingency plans, that can help you kind of "ignore" your oppoents skill level.
What I mean by that is if you prepare for the threats your opponent carries, if you are aware and somewhat ready for the potential dangers of your opponent's team, you can execute your gameplan in a way to mitigate the threat of these components, and if they are a great player they will have to move in direct opposition of your plan and pressure which is aimed at putting their threatening mons to your team at a disadvantage, and if they are a "bad player" and make strange moves you can't predict, by executing your plan you won't allow them to randomly get one of the earlier identified problems onto the field in an advantageous situation.
You'll never be able to map out every move from turn 1, because you can never perfectly predict your opponent. The key to this is simply being aware of potentially dangerous situations and predictions your opponent could cause. It allows you to pin down your opponents win conditions, and by doing so greatly improving your consistency.
Team analyses is probably the most important part of consistency, as its the key to risk management. It's impossible to build a team that isn't weak to certain pokemon, or more likely combo's of pokemon, so understanding how to observe the opponent's threats and how they can be handled by your team before the match even starts can lead to consistency in your later moves as well.
You have to be able to see your own team's weaknesses and strengths to do this as well, so make sure to take the time to look over your team every once in a while. Compare it to the top sweepers and walls, and see what plan you could put into action to stop them, or how they threaten you. Think of what combinations they would likely be in, and see if you could handle similar threats, like Exkiller+Swords dance groudon.
If you realize that Groudon can sweep your team if its double dance, unless you can lower it to a certain HP level and revenge it with extreme killer, you're much less likely to bolt strike with scarf zekrom against Kyogre, when outrage will do enough damage to allow you to revenge it with something else.
Another important aspect of this is predicting variables about your opponents team. Admittedly this is much easier to do against good players than bad, because their teams are likely to be coherent. But again, if you have a plan for likely threats playing well against bad players becomes easier.
If you see a team that looks like Arceus/Groudon/Ho-oh/Forry/Latias/Genesect in team preview, you can judge things about their team that aren't readily apparent. Obviously Genesect is the most likely scarfer. They also carry a hazard supporter, so their arceus is likely ghost, to spinblock. Their is also a good chance that their groudon is a bulky support set, as it is their best exkiller and rayquaza check, and the sun dependent ho-oh wants the most reliable sun setter it can find. With this knowledge in hand you can make a tentative came plan, and by looking at your own teams strength and weaknesses make sure you put more pressure on the opponent than they put on you.
