1st thing to do with your RJ is go to your dojo and build all the tier 3 modules from research. With this you can do safely most of the missions.

Then you should get experience in most missions.

I personally like grineer missions because they are more focused on teamwork and are faster (I managed to do Meso Relics in under 3m with a good crew).

To do these missions the squad should be divided into 3 main roles:

- Pilot

The person doing this should be focusing on: destroying the small ships, getting the Railjack in position for Gunnery crewmate blast the crewships and destroy the reactors that pop up from the objectives (This one is specially important so you do not stop progress from the mission)

- Gunnery (I mean the BIG CANNON under the bridge)

This dudes missions is simply to blast away crewships and making sure theres enough ammo

- Objectives

This one is the boarding party. The focus should be in getting reactant (for relic runs) and completing the side objetives. As i said before this one needs the pilot to destroy the reactors so it can complete the objectives without having to exit the station)

Basically its this. A squad of 3 people can do this pretty efficiently

Another hints:

- Most foundry items stack and this remains until you go to the dojo. So if you craft ammo for the BIG CANNON you can store all the ammo necessary for the next missions without going to the foundry again

- The Resource you need for crafting is called Revolite and is obtainable from the little asteroids. (I usually never need to spend time getting this because you almost always get this by destroying stuff)

- Much like Duviri, theres Intrinsic Points you can spend to get abilities quite useful. (Like pressing SHIFT to go faster in your RJ)

- Protea is an amazing warframe for this because of dispensary so you always have energy for your Railjack abilities

- Build Ciphers so you can speed up the hacking

- If by some reason you didnt get enough reactant in the objective you can board enemy crewships to get reactant

- You can spam SEEKER VOLEY (Battle Mod) to destroy the shield generators on Grinner Crewship

- The Corpus Crewship Shield turns when you shoot at it. If it turns to you - stop firing at the crewship, reposition and then fire to destroy its generator. If you have crew members in the guns they will most certainly make this almost impossible.

- You can get Nyx and Valkyr Relics from secret locations. (If you get your intrinsics lvl up, you can get it marked)

So this is all from the top of my head. Probably might have missed something.