Take your starter dragon and uevo it to the first uevo option. Combine it with a friend leader to make a team with 2x hp, 4x atk and 2x rcv. Stuff the team with on color subs. Generally, a goblin, a fighter, an ogre and a carbuncle will get you rolling if you have absolutely nothing else.
Farm dragons of the tower until you are rank 100.
Expand your box space if you can, try to hoard the dragon plants you will get here.
Roll in the pem all the time, lately it has had mostly evo mats and enhance mats, but outside of those events, you can get various upgrades for your color team. The ripper series, golems and healers are all straight upgrades from the team i mentioned before.
By the way, do your best to level your team and evolve them as much as possible. I'm assuming the worst possible box, so any favor you can do yourself can only be good.
Once you're rank 100 or so, push on through the normal levels until you get to "lava tube." Run that for a while.
You might start to get some plus eggs. Sick em on a trash mob for later. You honestly won't want them on your current team once you have better options later.
Move on over to technicals. Clear on through to castle of Satan in the abyss.
Run the first level of whichever color tier 1 tech dungeon suits your color. For green, it would be a new journey. Collect pengdras, level them to 10 using the carbuncle and chimera that drop there. Evolve with your Dragon plants. Enjoy the fruits of your labor in the form of gratuitous fodder xp.
Run challenge mode and sit on your magic stones for a godfest you like on a gala that suits your attribute.
Once you've got a few leveled subs, you should be capable of beating the ocean god of heaven. Don't be like me, bring a defense breaker or a gravity. Took me several hours on my first clear.
Mind you, the slimes grow up to be frustratingly useful. Nab a few, namely king baddie. Also see if you can snag a vampire. They will be useful later.
Survey dungeons can be a lifesaver. Honestly i beat all of the tier 6 dungeons with a bunch of rippers lead by ADKZ. Those were dark times for me. Still, adkz, jester dragon, echidna and some others can be useful for a long time. Verche and lilith come to mind as well, just less urgent.
Know that I'm directing you towards a devil team, which means that it sucks that we just got Satan yesterday, because he would be the main attraction.
If you can manage to farm ocean god of heaven, by the way, do that, collect plus eggs, and camp survey dungeons and collect evo mats for variety. You should be able to climb ranks like a champ doing this, but if it's a chore, lava tube is a fine substitute. Remember, the worse your box is, you'll have to put more levels in to get a good result.
Try to clear all the normal and technical dungeons you can. Eventually you'll find 40 and 50 stam dungeons, where you can reliably farm bosses. Snag a hera and whatever on color subs you can. Green might have an advantage here with 5 mechdragon fusion god canopus and highlander on tap. Either way, see what you can do about uevoing hadar for your devil team.
So at this point you're looking at making a team to farm king of the gods, and just enjoying the game while waiting for your number to come up for a descend you can tackle. You could try to make your devil team with hera for a leader. Goemon isn't awful hard with a thoughtful team, dragon zombie comes to mind, and there are plenty of ways to take down Satan when he tools around again. If nothing else works before then, a Satan team will be able to smash kotg, which will take you well past rank 300 and reel in a bunch of plus eggs and dub mythlits.
After that, zeus seems to be the contender for farmable descend clear.
Having said all of that, many rem pulls are plenty strong enough to get you to this point in the game, and most gods can do reasonably well with farmable teams. More than likely, your first pull is sufficient to get you through tier 6. I got a strawberry dragon, which was part of my ripper-adkz team,which actually hurts to type now that i better understand how awful their synergy is with one another.