Question: * Holding A♣ 6⋄
* Flop K♣ 9♣ 6♣
* BB goes all in on Turn.

If I flop a club on Turn or River, pot is mine for sure. I call his all in, miss the flush, BB has two clubs and takes it. Should i have called his him?

Answer: 
As @Chris said, this greatly depends on your stack. In addition, you don't say if you're playing *cash* or a *tournament*.

At the moment you only have a `6` pair as a made hand. This may be sufficient or may not depending on your stacks.

If you are playing a *tournament* and you're desperately low, say having `10-15` blinds, then shoving here is `never` a bad play.

You have 9 outs for the `nut` flush, plus 5 more for `2-pair+`. Therefore you have around 14 outs, which means `above 50%` to the showdown.

These kinds of combo draws (flush draw + pair, open ended straight draw + flush draw etc.) are pretty much the `nuts` when you're very low in stack. You're often ahead even against `TPTK (top-pair top-kicker)` like a `AKo` here with these monster draws (in this example, having the ace is making you a little underdog but you get the point).

However, if you're deep stacked, you're not desperate. You need to play the hand by paying attention to `pot odds`. Since you have `14 outs`, you have around `28%` per street to improve (say it's `30%`). A `~30%` pot odds is often created by someone betting the `full pot` `(33%)`, so if someone bets this or lower and have a deep stack, you know it's OK to call.

In your case, calling his all-in, you're not mentioning the `pot odds`.
The pot odds are calculated like this:

```
pot_odds = amount_to_call / (current_pot_size + amount_to_call)

```

If you end up with something below `~0.3` (30%), you know it's OK to call.

There's no standard way for playing this without additional input as @Chris said. For example, if someone have a deep stack and a call it's going to cripple him, it's probably best to fold as a `marginal 50%+ equity` is not quite much when have a deep stack, but it's awfully plenty when you're desperate.
If your opponent has the flush then you only have 7 outs so cannot call. 

If your opponent is doing this with a set or 2 pair then you can call.  

You have 14 outs and are right at 50% to hit by the river. 

You are at best 50% so I think you fold here.