This is something I've constantly struggled with. I never detail my comics to the fullest, because they're simple and clean, but I constantly forget I'm working zoomed out, and when I upload, they're big and every tiny mistake is visible and irks me to death. What sizes do you work on, per page, per panel? How do you avoid visible mistakes?
Aug '15
Feb '16
to avoid mistakes, I always work larger and zoomed in, then scale it down before uploading.
I draw Demon House at 8.5 x 11 inches, then shrink it down to 650 x 841 pixels.
I draw my other series at 6.625 x 10.25 inches, then shrink them down to 800 x 1237 pixels.
And I always work at 300 dpi and shrink to 72 for web publishing.
My working PSD file is 9.5" X14.5" At 300DPI (2850 X 4350)
That's to start, sometimes I do two pages so that's then 9.5" X 29"
When I upload to Tapsatic I resize it to 940px (which is max) and 98DPI.
DPI is the most important part.
I always draw larger then what I'm posting. You can always scale down but you can't scale up without compromising your work.
If you have questions about resizing your art feel free.
I scan A4 pages at 600dpi, and I do most of my work zoomed in at around 300%. I've met people who think it's excessive, but I love being able to work in very fine detail.
The only time I work zoomed out is when I have to draw a single line that stretches across most/all of the page. Otherwise, it's just for checking the overall image to make sure everything looks good as a whole.
I draw my comic Star Watcher at:
1880x2880 (26.112inchx40inch)
After I finished the page with text bubbles and such I "Save for Web" at 50% that size which is:
940x1440 (13.056inchx20inch) as TAPASTIC's max with is 940 pixels
The Satrians12 is actually a 2-page spread at 13.25 in width and 10.25 in height in 600 dpi. I like working with 2 pages at the same time- it makes coloring process much quicker. Plus, it makes it easy to place into Indesign file when you want to publish it. I know 600 dpi is a lot but hey more room for details and when it's shrunk down it looks nice!
When I'm done, I crop it to 6x9, flatten it, and shrink it to 200 dpi (so to prevent the PS from being slow when I do "save for website"), then click "save for website" and ta dah!
Grassblades-pages are 3307x4677 pixels in original size. Well, they're A4-sized at 300 dpi, which works out at 3307x4677. I then resize them to be 800 pixels wide when I post them on Tapastic. I do 800 instead of 940 because 800 pixels fits my main website better, and I don't want to have to do another re-sizing just to fit Tapastic - and it's still readable.
When I sketch stuff (I sketch digitally), I work zoomed out, to get a better overview of the page - but when I ink and colour, I zoom in a lot, to try to avoid gaps in the lines and mess-ups in colouring. I do still slip up sometimes, but since I resize them to be smaller, most of those mistakes are invisible to my readers. 
I work with pencils and inks on paper so maybe it won't be very useful, but for my webcomic Purple Boudoir, I always go with A3 paper (29.7 x 42cm = 11.7 Ă— 16.5inches), and a 600dpi scan for the colors. So my files are usually really big and heavy haha!
Working big is always the best, as a lot of mistakes will sort of "disappear" when the page is shrunk down (you've already noticed what the opposite does). But then you need to learn the amount of details you want to pour in your art. When I started using that size, I used to add way WAY too much stuff in my panels, just because the paper was big and it felt empty otherwise. But then when the smaller page would be ready, all of these details would either disappear or make the page unreadable.
Maybe you could try playing around with different kind and sizes of panels, and see what fits you and your style the best? 
I'm not sure what size my photoshop file is, as I downloaded a template (I think it's 300dpi), but I shrink down to 600 pixels wide for Tapastic.
I wanted to comment though mostly because a lot of people were saying they work zoomed out first to ensure the page looks good as a whole and I wanted to recommend something that's SUPER useful called the navigator - you may already use it or have heard of it but for those that haven't it gives you a little pop up window that shows you the whole page, so you can work zoomed in and still see how it affects the overall image! On photoshop you can find it by going to Windows > Navigator, but I'm not sure about anything else. They definitely have something similar on Paint Tool SAI, though! I find it useful because even though I sketch zoomed out, when I zoom in I tend to change little things when I'm cleaning up the lines, and this stops me from making it look awful by accident. d:
I have to resize all comics specially for tapastic. But original they are between 1500x1100 px. But it's too width for tapastic I have to resize them to 940x615 instead..
I work in a program called fire alpaca and I make my pages 9x11 inches in 300 dpi for all of my pages and I try to shoot for 8 to 7 panels per a page c:
I'm probably making a huge mistake that ruins my long-term options of printing, but I tend to work starting at 940px wide (the size limit for tapastic), and usually 1500px tall. It looks fine for web platforms, but can't be zoomed-in on or printed at high resolution. I only chose to work at 940 because it's faster to paint and easier for my computer to handle. As for panels, they vary in size greatly, but I never tend to make a panel bigger than 1/2 the page.
I will most likely be starting to work with a page-size something more print friendly when my next update comes around (although it won't be noticeable for tapastic readers because it'll be sized-down to 940px).
I don't like to draw in small spaces. Plus, it's never a good idea to work on a size that's the same as the one you're going to publish.
My pages originally are size A3 (29.7x42 cm) at 300dpi in resolution. This is a bit overkill, but I chose these parameters because I hope to print the series sooner or later. Also, the site where I publish the original italian allows larger images than Tapastic.
A4 for my comic (but it's very simple and with a very few details).
A3 when I am doing an illustration, or when I work on inking samples of illustrations and sequentials.
I'm work at a ridiculously large size then I revise everything down. I work on a 3425x4200 px canvas then I downsize to Tapastic's 940px wide size. Since my style is still pretty simple it can be easy to see the mistakes if you look hard enough but it works for me.
I always say start big then just resize it to fit your needs if you're doing digital art or anything online. Like my program tells me the percentage of the size I'm at and whenever I resize it's always about 25% of the original size.
A5 sized for mine and sized die to somewhere around 874 pixels? I don't know why I did it at that number but it makes the tones look better overall. I do A4 size for illustrations~^^b
I draw at A4 size then when I want to upload them, I resize to 1200px height. The reason for draw the A4 is oneday when I had enough pages, I would compile them and made it into a hardcopy book. Other advantages is when you resize to smaller size, it helps smoothing the lines and sharpen the overall images.
