Since runes are all meant for late game and samira has 0 base dmg on abilites, everything is just from her total AD don't be the first one to walk to enemy,let your support CC them before runing them down while positioning yourself and keep stacking [Manaflow Brand].

If they're in E range+enemies don't have much CC(2+)+your supp is close => go ahead

It actually starts the moment you get ult, keep safe (away from CC) while trying to stack passive, when you have 3, it's safe to dive, if enemy support is tank CC,wait for him to get away from ADC,dash/flash, finish stacking passive and ult while keeping them both in range.

Everyone tries to focus ADC and it's 5v5 on one lane, try stacking ult whenever you can, be the front (to the side, like mocking them to come get you in your team)

The moment you get oportunity, go in(flash EQ/EQ)(with 3-4 passive-R stacks) (if you wait 6, they will see your and will know your ult is ready and save CC for you, do stack 6 only if you want them to save their CC while others kill them),

press WR and walk around within them while KEEPING DISTANCE from MELEE CC,because people who rely on ranged CC are probably squishies that will die from R too fast to react.

You can now chose to dash with E(reset on kill) to chase down those low on HP or just E back in your team if there is someone good guarding them,if not, just chase them down one by one with E reset while positioing, AND , if you stack R again, they can pretty much say goodbye if they're not tanks.

Knockup after teammate's CC from Samira's passive counts as basic attack in combo.
It is optional to start by keeping distance, so spam Q untill you hit
From then, AA Q AA if your support doesn't have CC, you can just AA Q AA, get distance, Q.

When stacked, you got a lot movement speed so you can chase them down easely if you're with CC support(if enemy has tank support,chase ADC down first,even if Leona gets you, so long as you kill ADC you get reset on E).

Enemy is very carefull when you have a lot on combo count(4-6), so going in with (flash+)EQWR comes as quite surprise, especially if you flash and suddenly appear blasting their backline (EQW is 3 combo count, use it only if you have to because W is emergency windwall , but in this combo they don't have much time to react.

-Stack [Manalfow Brand] as fast as possible.
-Remember to ult whenever you can when you're in enemy team, ult has 5 seconds cooldown so getting S is as much of a problem as CD, if you ult on start of the combat you got time to stack while combat lasts so blasting enemy team with 2 ults would be nice.
-Remember that as long as they don't oneshot you later in game, as long as you're close to minions AND NOT CCed you can just slam Q on minions/monsters and instaheal to full HP, making them tilted and increasing ban rate on the champion.
-As long as you have some stack later in game(with good damage and lifesteal), staying close to front even with low HP is easy because ult aplies lifesteal and can turn combat around at any moment.

-Samira is late game champion, whose abilities have 0 base damage, and whose stats are around Yuumi's, so focus her down first even if her support is Senna who is know to be really squishy.
-Because of base damage, if it's 1v1 / 2v2 and she doesn't have CC support, it will be pretty easy to kill her with sheer damage in early game, altho if you're melee she can just dash through her minions after landing few hits and than chasing you back as punisher for your attempt of even trying to get close, but, if you can, keep close as melee.
-You need a melee CC to counter this thing, fight normaly and ignore all damage untill she ults, CC as fast as possible even if you have to flash at that moment, im sure your team will gladly focus her down after she threw her ult and has to wait for stacking again+probably doesn't have E so even if she uses W keep fighting because the moment you take distance, she will just stack again, ult and you'll regret your bad decision.
VERY IMPORTANT:Midle and late game she can heal astronomus ammounts from both her Q and ult so try to stay away from minions and jungle camps with big number of monsters or she will instaheal and counter your every pitifull attempt to kill her.