I always train to "show your working" for those first starting query building or those building complex groups:
Step 1
I want to see a list of people who are the primary person for their accounts where they are solicitable, have an email address and are either CEOs or VPs
Step 2
People where DNS is not equal to 'Y' and email contains '@' and (title contains 'CEO' or title contains 'VP)
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You could even take it one step further (and this is how SLX 7.5 web builds groups) by building up the columns you want to use first:
I want to see the Primary person column with a "Y" in it, the person's firstname, lastname, email, DNS without a "Y" in it...
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You can see not only how it helps identify exactly what conditions and operators you are going to use, but also whether you'll be needing brackets or not - Golden rule here is that if there is an AND and an OR then you will have brackets.
Incidentally, you might notice that I have used the "DNS does not equal Y" rather than "DNS equals N" this is because often, imported data leaves it blank rather than entering an N. I have also seen data imported and the DNS (and other checkbox fields) with other things (e.g. '1' instead of a 'Y').