This might sound a bit meme-ish, but it is a valid strat.
Most of 3v3 maps are rather big, so mobility is the key here. If you lose an encounter, then your units will have to sprint back across half the map spending a lot of time. So play around mobility!
Go with Overwatch for JLI or Luftwaffe for paratroopers & heavy emplacements.
kubel-kubel-kubel-upgrade for sturmpios-tech truck into mechanized - luchs + autorepairs - then it depends on the situation. I prefer to open with more infantry, but you can go MG or Raketen.
If you need a bit more firepower, go for early call-inf of JLI.
If you want to lock down a cut-off - put 20mm flak down.
Kubels do not bleed manpower, rather maneuverable, and they vet up rather fast when you use them togheter. Fisrt spread them to gain control, then bunch them up and bleed your opponents, sneak for cutoffs, outmaneuver your enemy.
3 kubels with a bit of micro can reliably kill clowncar. And if you lose them you can salvage their wrecks for a bit of fuel to speed up your LVs!
There are a lot of weaknesses like Vikkers, upgraded penals, you need to have a decent micro and so on, but it is super fun.
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