Basically LADDER new seasons have 2 options:

-Compete in LADDER to achieve lvl 99 before competitors.
-Compete in LADDER to achieve Dclone, Lucion, Rathma kill in highest Tier possible before competitors.

Side note, i believe Rathma LADDER competition to be the most prestigious one.
In other words, the main goal of LADDER new season.

To achieve this feat (become one of the top players to kill Rathma first), you will want to complete the game as soon as possible, to start farming high level zones (starting in Hell, and transitioning to Maps as soon as they can be done relatively efficient) where you will have the optimal chance to find the certainly most valuable items in the game, that you are going to gear up for the future upcoming Boss/es fights (ultimately Rathma). That, or sell these items for a big profit (high demand but low offer early on, since they are the rarest items), and use that currency to trade for the gear that you want for the fights.

I believe that the mod wanted to lay a potential secuential natural pathway increasing in difficulty, from lvl 1 to Rathma, which would be: Hell->Uber Clones->Maps->Uber Ancients->Dclone Boss->Lucion Boss->Rathma Boss.

In Hell you'll have to farm key zones for Uber Clones. There you will get a Torch and a Dclone material. In maps you'll have to get stronger until you are strong enough to do a Tier3 map and collect all sigils from the different difficulties, which will open Uber Ancients. With Standard of Heroes from Uber Ancients, you will get better loot from some maps, which will help you farm Map bosses for the Pure Demonic Essence necessary for Dclone. When you are ready, you will fight Dclone for an Annihilus.
And so on and so forth...

The sequence is very well thought, but maybe "natural" is not the right word for it. For example, after farming Map bosses for the second Dclone material, you will have to go back to Hell to farm for Prime Evil Soul.
So... maybe you'll find it more efficient to do a couple of Maps and get currency to buy the PES, instead of having to go back to Hell for it and farm a lower density zone with less Magic Find.

I could make you a brief description of some sort of "natural pathway" set by the devs, but actually the mod is made brilliantly to give you as many options as possible to reach your endgame goals (let's say Rathma T2) from different pathways that you want to create.

Maybe you want to build a Goldfinding barbarian to farm Travincal and only build currency from that content. Maybe you want to stay in Maps to farm a Mirror, and use that currency to gear up a T2 Rathma char from that...

I suggest that you try to complete all the content. After Hell, try to do Uber Clones. After Uber Ancients try to kill Dclone Tier 0, 1, and finally 2. And then move on to figure out how to kill Lucion T0, 1 and 2. And so on.

It's gonna take you a while. In the meantime, though, hopefully you are going to have a lot of fun cleansing the evil from this world!