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I live in western Saudi Arabia, I am trying to see the comet ISON, reading here and there tells that I can see it by naked eye somewhere next to the constellation leo, I used an app to tells me where constellation leo is but I could not see the comet.

Is it visible from Saudi Arabia? if so, in which direction (west, east, etc.) and what time is the best to see it?

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You could test this out by installing Stellarium (free night sky application: stellarium.org). Input your location and you should be able to see whether or not you could possibly see it. –  astromax Nov 19 '13 at 14:36
I also highly recommend Stellarium. –  dotancohen Nov 21 '13 at 8:53
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I'm not far from you (Israel) and I am also waiting to see comet ISON.

Comets are very unpredictable, and comet ISON has not yet reached the critical part of its journey which will determine visibility for us. Comet visibility is usually due to reflection of the Sun's rays on the coma and tails of the comet, as the nucleus is to small to see directly. So ISON's visibility (and all comets for that matter) depend on how much gas, water, and other materials that it outgasses. This in turn depends on how much volatiles it has, how much the Sun melts them, how much the slingshot around the sun and tidal forces fracture the nucleus, and other factors. So the actual visibility that will occur is very difficult to determine in advance. That said, ISON has all the markings of this being its first trip around the Sun. Thus, we assume that it has many volatiles to release and we assume that ISON will be exceptionally bright.

In any case, ISON will be most visible when it is closest to Earth, near the end of December. It should be most visible in the early morning sky, I'm guessing at about 4:00 AM or so. This is because ISON will be close to the Sun (thus visible close to the time that the Sun becomes visible). Like all celestial bodies, it will rise in the East. Each day the comet will move farther from the Sun and thus will be visible earlier and earlier in the night, until it disappears from view probably sometime in mid January.

You are welcome to visit Beersheba and have a peak through my binoculars!

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I think the term "most visible" is somewhat vague. Early (~5th of) December may be more favourable than later in the month, even though you'll have to observe it in twilight. As the days go by, you can indeed see the comet earlier, against a darker sky background and higher above the horizon, but the object itself will also be dimmer. You may therefore always need binoculars to see "ISON". –  AstroFloyd Nov 21 '13 at 8:44
By 'most visible' I infer the greatest visual magnitude difference between light originating from the comet components (nucleus, coma, tail) to between sunlight reflected from out atmosphere or direct from the Sun. –  dotancohen Nov 21 '13 at 8:53
Good, and I was wrong. I wrote a small program to compute exactly that: the "excess magnitude" defined as <limiting magnitude> - <comet magnitude corrected for airmass>, where positive values indicate you may see the object with the naked eye. I get (for Riyadh): Nov: Day time Exc.mag 15 4:56 -0.2 17 4:59 0.1 19 5:03 0.3 21 5:08 0.2 23 5:17 -0.4 25 5:53 -1.3 27 6:10 -2.2 (28 17:06 -50.7 - never visible) Dec: 01 6:15 -3.4 03 6:04 -2.3 05 5:57 -1.8 07 5:29 -1.3 09 5:23 -0.4 11 5:21 0.1 13 5:18 0.3 15 5:17 0.3 17 5:15 0.4 19 5:16 0.3 21 5:15 0.3 23 5:16 0.2 25 5:13 0.1 27 5:14 -0.0 –  AstroFloyd Nov 21 '13 at 10:08
@AstroFloyd: Please put that up on Github! I would love to see that, no matter what language it is written in. –  dotancohen Nov 21 '13 at 10:10
I apologise for the loss of format above (paste it into your text editor to restore the three columns). Summarised, the table indicates you could see ISON with the naked eye on Nov 17-21 and Dec 11-25, best around Dec 17 at 5:15 AST. The computer code is very simple and while I think that the best dates and times are roughly correct, the magnitudes are probably not and you may well need binoculars to see ISON as the original answer indicates. –  AstroFloyd Nov 21 '13 at 10:14
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