Again this varies a lot depending on where you are going, Los Angeles is cheapest around January due to it being the rainy season so you’ll find the cheapest flights to the USA then, Miami experience its off season from June to August as temperatures get very hot so cheap flight tickets are more readily available if you plan in advance and book them early.
Where Kiwi.com really shines is the way in which it mixes and matches airlines in order to find the cheapest price. For example, maybe you want to go to Rome, Italy from Washington, USA. A typical flight search engine will only suggest routes coming from a single airline and its partners. An example search on Expedia shows the cheapest route as $631.20 USD via TAP Portugal.
Use skyscanner.net. This neat website searches all airlines, big and small, and allows you to look for the cheapest rates out of your local, rather than getting bogged down with specifics. Meaning, if you know you want to go on vacation but aren’t too picky about where, this website will provide the cheapest flights to everywhere in the world from the nearest airports to you.
In Google Chrome or Safari, incognito is enabled by hitting Command (or “Control” if using PC), Shift, “N”. For Mozilla Firefox or Internet Explorer, hit Command (or “Control” if using a PC), Shift, “P”. This will open a new browser window where your information is not tracked, thus not inflating prices as you search. Note: if you're using an older version of OS X, open Safari then click “Safari” in the menu bar, and select “Private Browsing”.