Like DrNiggle said, you want to be efficient, considerate and speedy. Players tend to want to get sorties over and done with. But me, I got rules to preserve my own sanity / enjoyment:
Rule one: Meta, Meta, Meta.
Rule two: For minimum heart ache, do Spy missions solo, or at least with someone you trust. I usually give a PUG group two tries, then solo.
Rule three: Defence missions are painful without a competent team. This is probably the only time in Warframe you might want to actually discuss stuff before you start.
Rule four: It's always credits or a statue. Anything else is cause for joy.
Rule five: Don't bother if it's got a Defection or Archwing mission. Even if you're okay, PUGs will most likely not be and you can't solo them. I also tend to skip Lua Spy.
Rule six: Know the fights, know the phases and how they trigger. If you're not sure, read up or run the fight on normal before you start mission one.
Firstly, if you haven't already, have a look at
Warframe Builder.
Use easy mode frames with meta builds.
- Spy/Rescue - Ivara or Loki, maybe Ash or Volt. Just go, go, go like DrNiggle said. Don't attempt the room or a hack unless you're sure you can do it, and never "assist" anyone in progress. While the ciphers don't work, the Liset Air Support ability still does.
- Defence - CC frame (Oberon, Equinox, Sayrn, Banshee, Octavia, Nezha ) or a tank. Consider giving the Operative a Furis like this or a Hikou like this. The Furis will keep them alive, with the Hikou they can OHK to level 80. Atlas can block them into one spot, Ash can hide the target with smoke shadow, Limbo can banish them but you're more likely to find yourself alone in the mission once the other players realise you're a Limbo. If you're going to bring Nova to Defence, don't go overboard with the strength in either direction - you'll either prolong the mission or overwhelm everyone.
- Excavation / Interception - CC or area denial frames and weapons like Equinox, SlowVa, Banshee, Vauban, Frost or Zenistar can be great here. Stay on target unless asked or reviving. One extractor at a time. Use your Specters.
- Survival - Combos like Ivara with Dark Dagger / Covert Lethality / Gleaming Blight or Inaros and Prisma Dual Cleaver / Justice Blades can be really useful for survival. Remember that the shades that Nekros' Shadows of the Dead count toward the total numbers of enemies in a survival - raising too many shades will decrease the number of personal life support modules dropped.
- Everything else - use a tank with moar dakka. Iron Skin Rhino, Vex Chroma, Inaros, etc. Atlas with a crit Hirudo can be fun on Infested Exterminate / Survivals
- Never take Limbo unless . .. you, ... um, wait, you know what? Just never take Limbo.
Weapons should be meta too. SomaP, Arca Plasmor, Dual Grakata, Lenz, Sancti Tigris, AkStilletto, Kulstar, Vaykor Hek, Zakti and Glaive, Atomos, Atterax, etc. My preference is for frequent big ba-da-boom or combo builders.
Look at the modifiers and cheese them. <Weapon type> only and you suck with it or don't have a good build? Excal, Titainia, Sayrn, Nidus can cheese around it.
Know the fights. If you're going to try Fatal Teleport and a Dark Dagger / Covert Lethality kill on Zanuka, tell us and have a backup to do it normally if you can't do it - and don't take Saryn to that fight, you're just making it harder for everyone. Don't be afraid to cheese the Raptor with the Rhino Stomp trick, just revert to a more basic strategy if you can't pull it off. Be especially careful with the Multalist Alad V fight, Ash can wipe your team out in seconds, as can anyone who brought an end game Lenz or Opticor.
Use your gear wheel. Specters spawn at the same level as enemies. Pherliac Pods are not just for that one quest to get Atlas. Ammo, health, shield and energy pizzas are cheap.
Use your >Spoiler< Mode. It can get you out of, or around, a lot of trouble.
Consider your companion choice. I usually go Carrier for it's survival and ammo mods, or Helix for marking weak spots. I know cats and dogs can be useful, but I've never found them better than having vacuum in a sortie.
Finally, don't sweat it or burn out. I managed to get the sortie down to about 20 minutes at one point, but it wasn't fun - more like a daily chore. If it looks like it might be too much arse, leave it until tomorrow.
way better than what it was and gives us plenty of room for expansion.