If your mid lane is an Yasuo/Zed/Talon, don't pick Riven/Tryndamere top or Rengar/Shaco jungle...

...and vice-versa. Or any squishy melee AD champion for that matter.

There is already an AD assassin on your team. What makes you think that your team needs another AD assassin?

If you really want to pick an assassin, at least pick an AP assassin such as LeBlanc, Ekko, or Fizz. Picking another AD assassin will just make it very easy for your enemy team to just pick a tank such as Malphite and Rammus (I mentioned them because they heavily benefit from stacking armor) and counterbuild your team. Also, it really limits your teammates' choices. For example, imagine there is a team with an Yasuo mid and a Riven top. This forces your jungler to decide between picking an AP jungler or a tank jungler. They will probably pick an AP jungler and force the support to pick a tank support - even though the player that goes support is way better at playing squishier supports (Soraka, Sona, Lulu, etc) than tank supports (Leona, Thresh, Braum).

I say that because I got tired of going into battles where people don't care about the team composition and just instalock Yasuo and Riven, limiting their teammates' choices and making the team fall off late game because they have two early game champions with roles that overlap with each other.

It's okay to pick an AD champion for top/jungle if your teammate picks an AD mid laner, for example, as long as that AD champion is tanky and your team can compensate the lack of magic damage elsewhere. For example, picking a Darius or Renekton for top lane. But Riven is squishy. She essentially has the same role as Yasuo, picking off enemy carries and bursting them down. While she does that in a different way, their final goal is still the same.

We are not on the end of season 4 that was known as League of Assassins because teams with 2 or even 3 assassins were viable because tanks were weak at the time and bruisers had poor itemization.