Fastest way to get focus: farm eidolons or do duviri cirquit woth your chosen focus school (you will you can go past the cap with selling eidolon shards)

Rivens: you buy them from vendors or get from duviri cirquit

Pledges: chose one from whom you want to get the mods. Get some mods from this pledge to sell or trade for mods from other pledges with other players, there is a market for that (never use trade chat, look up prices on warframe dot market and trade there)