So I just started this game. Put a few hours in so far. It's fun, but honestly, what should I even be focusing on at low levels?
I would say the most basics of things are:
Right when you get started you can just follow the quest prompts.
After that its never wasted working through the planets to get to the relay to the next planet.
A level above that:
Gear is master rank (level) locked, you gain master ranks by getting gear and then leveling it up once/ item (no point in crafting - maxing - selling - repeat the same thing).
Your weapons and mods make all the difference in the world.
Mods: Mods that say "Damaged" are just newbie things that drop in the beginner quest (vor's prize) and get replaced with better undamaged versions, alltough in the grand scheme of things upgrading these is a small investment in the end...The mods that drop early and stay good for a long time so not a worthless investment are warframes + health and + shields and weapons + damage, and other pretty straight forward stuff...a little later you will want the 5 power mods of flow, streamline, continuity, intensify and stretch.
Weapons: Off the top of my head. You can get some pre built beginner weapons from your arsenal for cheap which is good cause you can use them as master rank fodder, except the Lex pistol which is good. For most weapons though you need to buy the blueprint from the market (dont get fooled like me and assume its just for real money purchases) with credits and then build them in your foundry, the Boltor Rifle and Hek shotgun are good early.
I could go on but i ran out of steam and this started feeling like word vomit..I'll just end by saying if you have amazon prime, or can start a prime trial you can link your amazon prime -> twitch -> your warframe account to get some good stuff.