Off the top of my head:
1. Pick Excalibur. Not only is it the best starting frame, farming it later is an unholy pain in the ass compared to the other two. Spend your starter plat on a warframe slot (20p) and four weapon slots (2x12p).
2. Don't invest anything in damaged mods. If you need a set of the most important mods to have at the beginning I can hook you up. Basically Vitality, Serration, Point Blank, Pressure Point, and Hornet Strike. Your ability to trade is very limited at low MR and I can only trade 5 things at a time, but it does reset daily (at 1900 EST).
3. Don't waste a lot of time in Cetus/Plains. They shove it in your face very early because it's new, but it's pretty much a self-contained area and it will stunt your progression with everything else.
4. Always be leveling stuff. You can't just find a frame/weapon setup you really like and use it all the time, because you gain mastery ranks from leveling up frames and weapons to 30. Build a weapon, max it out, sell it, and grab another one from the market or your foundry. Most need to be built on the foundry from blueprints and resources but there's a few (MK1-______, Lex, etc.) that can be bought for credits. Frames always need to be farmed and built, and they're enough of an time investment that you should never sell them unless you get a direct upgrade to the Prime version. Choose wisely if your slots are limited and you're not buying plat.
5. Build a Hek shotgun as soon as you can (MR4). Keep it forever, ideally get a Scattered Justice mod for it, and use it whenever you need to do a mission that seems too difficult to complete with crappy guns you're just using for mastery fodder. Same goes for Galatine which is a big ass sword usable at MR3.
6. Watch alerts for aura mods like Corrosive Projection, Energy Siphon, weapon mods like Blaze, Shred, etc. and especially Orokin Catalyst/Reactor or Forma blueprints. If you see an alert for one of those pop and you don't have access to that planet yet, ask someone to taxi you there. I have everything unlocked and can get you through just about any mission (Svieri in game).
7. Join the Rerolled clan, and immediately build the dojo key so you can travel to it.
There's probably a bunch more stuff I'm forgetting, but it's really hard to remember what WF is like for new players when you've been playing for years and have basically everything. I can answer specific questions you have though.
Edit: if you've got Amazon Prime be sure to set up Twitch Prime and link your Warframe account to it. You'll get one of the most useful warframes, an excellent rifle, and a decent melee weapon. They come with slots and potatoes (slang for the things that double the mod capacity from 30 to 60) so there's no downside at all to claiming them. Just remember what I said above about not trying to stick with one particular setup.
