Assumption: you are completing offers legitmately, with real information, and for the first time.
From a technical standpoint, nothing in this thread could possibly help your crediting. In fact, the cookie deletion is much more likely to hurt your chances.
Look at it this way: these tracking systems have been around for many many years and are designed by the marketing companies that use them. It's in that marketing company's best interest to track as many completions as possible, since that's how they get paid. Therefore, the tracking systems were designed so that they track perfectly on a standard, out-of-the-box configuration. And they do.
There are two main methods by which an offer can fail to track:
-> The advertiser's computer system may choose to not fire the tracking pixel. They are allowed to do this, and although the criteria are usually stated up front, sometimes they are not. Example: If a particular company owns several different sites, they may choose not to fire the tracking pixel if you sign up on more than one of their sites. [We try really hard to avoid putting conflicting offers up but with dozens of companies and hundreds of sites it is extraordinarily difficult]. Another example: if you've signed up at a site before, and you sign up again, they generally will not credit you.
-> Pixel tracking has an inherent and insuperable design flaw that causes it to track less than 100% of the time. This can happen for a few reasons: Flow interruption, blocking, HTTP request failure.
--> I believe blocking is the most common cause for noncredit. I use this term to mean the blocking or deleting of the tracking cookie. This can and often does happen silently. It's usually a "feature" of ad-blocking, anti-spyware, or anti-virus software; or sometimes a setting in your browser; or sometimes it is done by hand by people who think that they are helping themselves by deleting cookies.
--> Flow interruption occurs when you complete an offer's requirements, but do so via a different "path". An example of this is Obopay - if you sign up but their system cannot verify your identity, it will request that you call them and fax them a driver's license. Once you do this, your account will be activated (and thus the offer requirements met) - but you will not be credited. That's because you never see the normal "account successfully activated" page - they activate you manually via the DL fax. There's just no working around this, sadly.
--> HTTP request failure. When you get to the page on the advertiser's site which meets the completion requirements, the advertiser's server instructs your browser to download an invisible "pixel" image which handles the tracking. If you press "stop" (or hit the escape key, back button, etc) before the page is fully loaded - the pixel will not be fetched and the offer will not track. Occasionally, the request to fetch the pixel will fail for an unknown technical reason. It's the insuperable nature of the protocol that the failure happens silently, and it doesn't get tried a second time. In that case, the offer will again fail to track.
Sorry to get so technical. This is mostly my opinion, but I base it on a significant pool of data and experience from a 2.5 year period.
Bottom line... use your regular email address and contact information in a fresh installation of any standard browser, without any adblocking, antispyware or antivirus software running, and you're golden 99% of the time.