It is very easy to think that when your website goes live you'll just deal with enquiries in the same way you'd deal with any standard enquiry - but the world of the web is a strange one, and people have very different expectations.
The moment you put an enquiry form or method of electronic contact on your website - you should be thinking about the standards you are willing to meet and the service you're going to deliver.
The internet brings with it a level of expectation and it is mostly geared around speed. Your potential customers want a swift response, whether they know it or not. You need to plan for that.
Don't be too hasty
Ah, the old addage of don't be too easy. Utter rubbish and easily countered by the argument of time waits for nobody. Do you seriously think you might be the only website they visited and made an enquiry through? Getting the first response, even an acknowledgement of the receipt of their enquiry, is the biggest single way of letting your new potential client know that you're on the ball.
It can be 11pm at night when you receive an enquiry and you need to be able to receive that enquiry if you're not tucked up in bed. Make sure that you're in a position to get enquiries remotely. It does no harm to let a customer know with a reply that you've received their enquiry - you don't need to give an immediate in-depth response at unearthly hours, but giving them the acknowledgement that you're dealing with their request can make a world of difference.
Why does it matter?
The internet opens up a world of possibilities, but not exclusively to you. Your potential clients have a far greater number of options available to them and creating an impression that makes them favour you from the outset is an incredibly important one. You can have the nicest looking and most functional website in the world - but if you don't react to enquiries in a timely manner you needn't have bothered spending the money on your website in the first place.
The open all hours scenario
The web doesn't wait. Your website hopefully doesn't stop accepting visitors once you leave the office! So, should your customers really have to wait until the next day for an enquiry? The chances are that most of your competitors make them wait.

That represents an opportunity. If you decide not to take it then you're missing one of the most useful weapons your website has given you - the convenience of access for your customer base.
It doesn't take a genius to set up e-mail on a mobile phone, via a laptop or on a PC you use at home. Nor will it ruin your life if you make a point of checking the mail on a mobile phone once an evening - you'll still have beaten your competitors to the client.

Unless, that is, they're reading this too.
Don't wait, plan for it. If you're going to invest in a website or already have one, give very serious thought to your customer service ethic and live up to the expectation that the internet has given the world - the tomorrow is too late expectation.
If your website doesn't have an enquiry form of some type, make sure you get one. You can't presume someone will be comfortable clicking on an e-mail address and writing a fully blown e-mail enquire to you.

Make the process simple. Forms are quick and easy - and they also allow you to direct the way a potential customer structures their enquiry. So, you get all the information you need from them in order to respond appropriately.
Furthermore, how do you know your customer is even browsing your site from a device they have mail services on? They could be browsing on a mobile phone with a mail account. Clicking on your e-mail address won't open up an e-mail to you if they don't have the software required on their device! But a form - well that'll do nicely.
Not everyone wants to type a subject header, put in the effort of explaining what they're enquiring about etc - so yet again a form with drop down boxes or preset options has a distinct time and ease of use advantage over the plain e-mail address on a website.
You don't like forms?
Interestingly, it isn't really about what you like. It is about what encourages a visitor to make an enquiry. One of the biggest mistakes new website owners make is by asking for a solution that they like instead of what the market demands.