There have been a few times where I’ve lost because the opponent really just outplayed me/did something cool, or I won despite the opponent playing really well

I’d really like it if on the win/lose screen you could say “Well played!” Or something

(I wouldn’t messages that say “too bad” or something, people would spam that)

if you are an experienced player, feel free to skip/ignore this post. I aim this to the new to semi experienced crowd who might be struggling a bit to rank up.

Before the game starts

Try to identify the core members of your opponent's team. Cores are typically bulky Pokémon that sinergize well with the rest of the team in order to survive a few turns or dish out some good damage to a decent chunk of the meta.

Identify their leads next. In VGC, leads typically trigger effects immediately upon entering the field or on their first turn, like setting weather, tailwind, trick room, intimidating your physical Pokémon or simply threatening with a potential fake out. Most teams have 2-3 leads to choose from.

Based on this information:

• Can you disrupt their core(s)? If they are playing a gimmicky off-meta team for BO1 ranking sometimes you just have to do what you can, but you need some form of counterplay for meta teams. If you don't have it, adjust accordingly after the match.
• Don't pick exclusively for counterplay. If you mess up your reads or your opponent overpredicts, you will be in a bad spot. Play around your own core and pick the leads and disruption that you find most useful against their team (in terms of typing, speeds etc).
• What mons can they mega evolve and what do they trigger when they do so? Since mega Pokémon have high stats, most teams have at least 1 mega evolution in them. Sometimes they might have 2.
• Pick your team in such a way that you can pivot comfortably. Have something in the back that helps you react to what's happening on the front (ie. shutting down weather or balance out the typings in a bad matchup).

If you do this correctly, you should be able to pivot your team and set up for damage within 1 turn. If it takes longer or the damage you deal is poor, you may want to adjust afterwards.

During the game

Turns have two phases: planning and committing. You have about a minute to plan. If you commit too early you are just wasting your resources —and if you have a clear shot, chances are your opponent can read it and react. Even top players take a long time to take notes and plan their next move.

If you do take notes, try to keep track of the opponent's...

• ... moves and PP (you can do it as IIII II and so on)
• ... mons they revealed and their HP%, since they might switch them out any moment (edit: forgot to mention Champions does this for you! always keep an eye on it)
• ... mega evolution status
• ... mons who protected last turn

The way most turns play out, people can either act, react or a mixture of both. You act when you have the opportunity to do your thing (set up an effect that's benefitial to you or swing for damage) and you react when you disrupt the opponent's play (you protect, call in a mon for countering, cancel out an effect or otherwise respond to their past or future actions) and more often that not you pivot and deal damage at the same time.

Based on this information, consider:

• Check the battle status often by pressing X. This keeps track of field effects for you (tailwind, TR, weather and so on) and even some per-Pokémon statuses as well. Sometimes it's a good idea to stall out an effect if that frees you to dish out damage later.
• Figure out the general play that's most benefitial to them. Early game is usually for positioning/setting up damage and after 1-2 turns they will want to both act and react.
• Figure out the specific play that's most benefitial to them. This has to do with what protected last turn, what mons they have in the bench and the duration of field effects.
• Don't be too eager to counter. If you mess up, you might lose a valuable asset. It can be benefitial to let them do their thing and shut down whatever they did later.
• When you prime something for a kill (ie. switching to a mon that counters their core) your opponent can read that and will react if they are able.
• Don't expose your cores or play them together, specially when pivoting or setting up a specific situation. Cores should Protect when the coast is not clear. Use mons in the back to help your cores by intimidating the opponent's team or enabling action on switch-in.

Some additional context that might influence your decision-making:

• Teams are woven together as a coat of mail. Strong, but easily torn apart when a link is missing. This is why great players play defensively and take their time, accounting even for potential crits. Try to take out easy mons first if you can, and corner their team into a suboptimal situation.
• Ladder is usually a bit more aggressive in early ranks, whereas tougher players play slowly. This is because rapid damage-dealing plays have more (and clearer) counterplay.

After the game has ended

Do not blame it on RNG. That's mostly out of your control, except for maybe attacks (*).

Instead, think:

• Was there a specific Pokémon, typing or team archetype that gave you trouble? If so, how common is it in the meta?
• Did they read you because they were good, or because your course of action was too obvious?
• Are you enabling your win condition consistently?
• What specific turn primed you for a loss?
• Based on the information you have now, what would have you done to prevent the outcome of said turn?

(*) Attacks are usually balanced around base power 100. Attacks under BP 100 typically have a chance to trigger an extra effect, whereas attacks above BP 100 compensate with lower accuracy, recoil or a debuff, like Close Combat. Players usually take these attacks only when they're a requirement to land a specific, pre-calculated kill, or the mon doesn't have access to anything better.