I realized that I have many wasted clicks which are not converts at all. On the other hand, I'm targeting really good keywords. The problem could be that my ads are appearing on many variations which doesn't really have anything with my ads so I should found negative keywords.

I found one efficient way how to do that, by typing your keyword in Bing search and exclude related keywords, but I think that's not enough.

Do you know any other way how to determine negative keywords for certain keyword?

Just examine your own ad campaign and use the words/phrase that do not convert.

It sounds like you are using broad match which is fine for initial setup, but you then should refine the words in the campaign(s) using the results you get.

Ok but my ads are appearing for some really strange keywords.

For example, if I'm targeting phrase "free slots", my ad is appearing as well for "SIM Slots Free Games" which is totally out of my audience, and many many other not targeted... So, the question is how can I know what all variations of kw's Google uses for appearing my ads?

I spent a lot so far and it's not converting at all, so probably the reason is there are many wrong kw's which I should use as a negative.

Not sure this will help, but in my experience (depending on your industry) exact match type will ensure that you are not over spending due to irrelevant clicks. If you feel like you are not getting the best out of your campaign with this match type, switch to phrase match. I tend to do my best to stay away from broad. When you get into phrase and broad, you will experience irrelevant clicks (broad more so than phrase). There is a way to see exactly what keywords users are searching for that trigger your ad(s). The manual way, I cannot remember. But I just pulled this from a Google forum that will basically return the same data:

"Run a "Search terms" report to see all the search queries that have triggered your ads. If you see any irrelevant terms, write them down and manually add them as negative keywords to your ad group or campaign."

Once again, depending on your industry and how you have your group/campaign setup, you will need to determine if said neg word(s) need to be set at ad group level or campaign level.

I am unsure of your Adwords experience, but I feel it might help if I add this little tidbit regarding match types.

EXACT: [new york restaurants] - Your ad will only be triggered if someone searches for exactly that.

PHRASE: "new york restaurants" - Your ad will be triggered if these three words are paired together on the user's search, however your ad will also be triggered if they have other words before and/or after this phrase.

BROAD: new york restaurants - Your ad will be triggered if any of these words appear in the users search in any order with any other word(s). This is were it can get super messy if neg words are not applied.

I hope this helps.

UPDATE: When viewing your keyword list, there should be a button that says something along the lines of "See Search Terms." Click on this and select "All." This way you can bypass running a report as described above. This will give you a list of keyword phrases that triggered your ads. Cheers.

BROAD can make my ads seen by more people, but it is also difficult for me to set the negative keywords one by one. Dilemma!!!