@W.T.
Here are some tips based on my experience with the Lv 50 All mode of the Survival Battle.
1) When you realize that the pool of Pokémon being used in the Courtyard Colosseum is rather shallow, then dealing with the trainers there wouldn't be so hard. As long as you know how to deal with those Pokémon, then you should be able to survive. Honestly, the same Pokémon tend to show up A LOT.
2) The wheel's layout never changes, so all you have to do is to aim for one specific spot every time. Release your dart when it touches the area between the green and white wedges. You'll most likely end up with the Complete Restore All, HP Restore All, or the Status Affliction Restore All options. (But of course, you will want to aim for the Complete Restore All.)
3) *Personal Experience* When you get to higher levels, you'll notice that going on the brute force offensive won't work all the time. Some hard-to-take-down Pokémon like Cresselia (Double Team, Toxic, Future Sight, ???), Spiritomb (Calm Mind, Dark Pulse, Hypnosis, ???), Lapras (Substitute, Whirlpool, Double Team, Perish Song), Froslass (Double Team, Hail, Blizzard, ???) tend to appear a lot in some of these trainers' teams. My Leech Seed-Protect-Leftovers Ludicolo loves stalling those Pokémon.
No, I'm not suggesting that you get a Ludicolo with Leech Seed. The point is that having a variety of strategies on your team has its advantages as it helps you adapt to different situations.
4) Always keep the fog in mind, but don't let the fog make you scared. Getting scared ruins your focus.
5) Think like a competitive battler, I guess? A competitive battler takes note of the strengths and weaknesses of both his Pokémon and his opponent's Pokémon. He also takes note of the status of the battle (weather effects, status ailments, etc). From these, he should make his decisions accordingly.