When I load my pages, I see the ads are not showing up and there is this message at the bottom of Chrome saying that the browser is waiting for
googleads.g.doubleclick.net. How can I speed this up so the ads display quicker? Is something wrong with my domain?
Any latency you see may be due to your network or any part of the Internet between Google and yourself. As well, for shared resources such as social buttons, you will see significant lag times. This is due to the demand for those resources and the capacity to deliver the resources. Google is rather robust and can deliver ads fairly quickly, but because of higher demand or latencies in the network between Google and your computer, it is delivered a bit slow.
This may not be the experience of your users. If you experience latency, it does not mean that you site users are experiencing the same latency.
Unfortunately, there is nothing you can do to speed things up in this case.
Even Google has a delay for these ads so, personally, I wouldn't worry about it. In fact, I use an ad blocker like 95% of the rest of world because no one want to see those anyway. If you really must alienate your users quickly (as opposed to slowly) then you should just cache the next set of ads and display the cached ads straight from your server.