Main thing I would say is that Copy and Paste is your best friend if you have a lot of similar products. You can create a "what I call default" product that has all the main setups in it for all the products that are similar to it and then use that one as the base for them all. In other words, if they share Optional Fields, similar descriptions, etc. make a first product then copy and paste that product to the same or a different category and you won't have to retype all that stuff. Edit what you need for the new product and alter the images and you're done, pretty quick work if you have lots of similar products at all.
Another thing that saves a lot of time when editing specific things is the Grid which is a table structure of all the fields of the products. Basically excel spreadsheet like and editable in multiple fields at a time so that is a time saver many times too.
Realize that the shipping and tax system is pretty much a manual job and then you won't be disappointed when you find that out after the fact. It's a daunting, in fact the 'most' daunting part of the entire program. Get your mind around that part and have your data ready to go for it and you'll be set other than a bit of time to enter it all.
Code for the HTML Tool isn't exactly the same as you would do on a current website. Some is kind of old school so it can be a bit confusing. One of the most asked questions is how do I center something. In short it's:
[[[<center>]]] put your text here or image or whatever [[[</center>]]]
The program's HTML Tool will always add the square brackets above to any and all HTML that it inputs. You can do this manually yourself too so you don't always have to use the tool, but it's a good idea anyways in case it will display the results instead of the code which sometimes it does and sometimes it doesn't, depending on what you're adding.
When adding code to something like an image, you can put the image URL in the code if it's external or you can put the image on the page then add the center or whatever codes around it. That's probably the most confusing part about adding functions of any sort to an item on the details pages etc. Add the item, then format it how you want it using the HTML Tool or just type it in there as above. Coloring text is done using the tools above the text box area, but to center it you need to enter the center codes as above "around" the text you typed, so don't add the text to the HTML Code or there will be no color formatting.
Hope those little tips help some.