Your most important skill as a writer is clearly your ability to convey your ideas clearly in a way that keeps the reader’s attention. Before you can prove yourself though, you have to get them to commit to reading your work. For that, you need a solid start. That requires a powerful first sentence and a gripping first paragraph.
It doesn’t matter if the person reading is an agent, your editor or the reading public. Judgment comes quick, along with rejections. Most agents and editors are reading hundreds of queries every week and as many as a dozen manuscripts at any given time. Granted most try to keep the number of manuscripts manageable, which means it is even harder to get them to give you a shot. Readers on the other hand are flooded with book options and usually your preview is all they will see unless you absolutely wow them.
So here is my suggestion. Make sure your first sentence has a powerful impact without being gimicky and your first paragraph is strong enough to pull them in. The odds of keeping them reading is so much higher if you can hook them from the start. If it takes until the second chapter to really offer a hook, they’ll probably just set it aside without ever getting that far.
Don’t start with something gory, overly sexual or offensive and think that is the same thing as creating a hook. Most editors absolutely hate stories that start out this way and most readers will assume the entire book is the same as the start. Also avoid weather, as that has become painfully cliché. Challenge the reader’s expectations in the first sentence, then move on to hint at great things to come if they continue on.
Even the best authors sometimes fail to manage this. Fame helps you get away with less impressive starts since the expectation of quality is already in place. We newer authors don’t have that luxury. Write something powerful and try seeing if it catches any attention among your critique groups or beta readers. If not, consider how you might rework it to increase the impact. You won’t always succeed, but being aware of the need for a solid start is going to greatly improve your rate of success overall.