Firstly, free books - standalones - don't work (except for series, where giving the first free is still a good marketing tool). You get downloads, yes, but the conversion to read throughs is woeful. Like most writers, I have a stack of free books on my kindle app - I'll read two of them because they're from writers I want to support. So the analgram of free being the way to do this doesn't stack up.
A couple of weeks ago, I put Inish Carraig down to 99p/99c for two weeks from its normal $3.99/£2.25 (or thereabouts.) My theory was I'd get higher rankings and more KU readthroughs - which net me more than a sale, anyhow. Because this meant I was on the 25% instead of 75% royalty rate, I was getting about 28p a book as opposed to my normal £1.70.
I did get a quick spike, but then sales fell off. So, too, did readthroughs. I put the book back up and it's selling away nicely and readthroughs have come back up.
I honestly think writing the next book is important, but so too is write a good book. Don't rush it and miss out adding depth and polish, which, for me, only time gives. Don't skip editorial.
This morning, I - or rather, Inish Carraig - was nominated by someone (who I don't know, but who had left a good rating on Goodreads a few weeks ago) for the Hugo awards*. One of the things they put in their review was that it had clearly been proofread (Inish Carraig is self published, where my other books are trad) and that that had made a difference. (They said other nice things, too.) That nomination, even assuming it gets no further as I expect, is a mark of quality that I carry into my other books - someone thought it was good enough to mention.
On another, related note, I've also been included as eligible for the Campbell award** (yesterday, as it happened, this has been an astounding weekend). To get this I either had to be published by a SFWA eligible publisher (I'm not, there are very, very few publishers who are eligible) or have a short story published which paid both .03c per word and had a minimum advance of $50 to a market with a set-minimum readership. That's quite hard to achieve for a new writer - and this is a debut writers award - as that's a pro rate.
I won't get many sales from all this. I do get exposure. (That old chestnut...) On multiple platforms. But, more importantly, I get people realising I might be able to write. When I go a-agent-hunting again, all this will be important in the writing cv.
So, how to be an author in the digital age? Write as much as you can, across various platforms. Write it as well as you can, remembering that you don't know what a small piece of writing (in my case a 2000 word commissioned short) can lead to. Price it for the market. And then hope for that little piece of luck you need. The marketing is secondary to all this - because your early marketing is mostly you saying "Read me, I'm great!" and that sells nothing.
*Cake is planned
**And fizzy wine.