Broadly speaking, you can divide arena into two buckets - either you go first, or you don't care if you go first.
The first bucket is much simpler to decompose. Remember that your goal is not necessarily to win against someone else who is also trying to go first. That's a losing battle. Your goal is to go before the people who don't care if they go first. So, your team is going to need someone fast-ish (>280SPD), and your team is going to need someone to control the other team. That second objective is probably also going to require an enabler - an ACC up champ - because otherwise you'll need absurdly high accuracy alongside agood amount of speed. And, lastly of course, you'll need someone who can win you a fight - but typically not one who can just outright win in one shot, because you won't necessarily be able to debuff the other team in the process.
A good example of a classic version of said team would be Kymar (lead) + Kimi (fastest) + Serris (debuffer) + Rotos. But, this sort of team has somewhat been losing favour, because it's just not reliable enough to actually win fights, especially vs the prevalence of Stoneskin/etc. If you really want to go down this route, I'd recommend only doing so if you have Leorius, Baron, or Georgid. The other traditional nuke champs really don't play well anymore in the current meta.
The second team is much more complex. Calling it a "go-2nd" team is outdated terminology - hence why I rephrased it as "don't care if you go first". The old goal was just beating the traditional Arbiter speed nuke team, but that's far too simplistic nowadays. This second team comp I'll divide into two further buckets - "gimmick" teams and "normal" teams.
The "gimmick" teams are easier to plan out - we're talking Cardinal, or full Stoneskin Lightning Cage, or other similarly gimmicky setups (Tormin, etc). The goal here is just to wait out the other team, and then "win".
The "normal" ones are your old, traditionally go-2nd team setups, where the job is to survive the other team's initial burst, and then outlast them over a longer fight. In this bucket, of primordial importance is some way of being able to survive that initial burst, if you're planning on fighting a speed nuke team, and some way of delivering sustained damage if your goal is fighting another "dont-care" team. There's basically two ways to accomplish this - either have a cleanser with really high resist and speed (Mithrala is a good example), or have a bunch of Bolster + Shield setups alongside someone like Brogni to provide even more mitigation.