nicky flowers

goauche is super similar to watercolor (a lot of people use both on the same paintings), so a lot of tips for that will work similarly, although obviously it won't be exactly 1:1 since goauche is less transparent.

i recommend checking out james gurney's blog for gouache tips, he uses it a lot and has a buuuunch of stuff on his blog that would help! (altho its also possible it might be a little overwhelming to just start wading thru the tag) https://gurneyjourney.blogspot.com/search/label/Gouache

this might come across as glib, but if you're first starting out with painting, begin by practicing washing your brushes. you will save yourself money and headaches getting your technique for this down pat.

the water ratio stuff, make a practice/technical piece where you try mixing swatches from no-water to 100% water. feel it out. just a lil strip of paper or journal for this, no need to bust out the good cotton rag.

composition, perspective, color: there's youtubes for these things but like. you can also just feel it out, try things, see if you can reverse engineer someone else's work.

gouache specifically, it is usually watercolor (pigment + gum arabic or other binding agent) with chalk or another opaquing agent mixed in. Really good gouache will use honey rather than gum arabic, allowing you to re-wet/re-work a piece better than gum arabic allows.

some technical things to watch for: on the tube, it will almost always list on the back several pigments; these look like "PB29", "PV5", "PR101". You can look these up and see how they do for lightfastness, opacity, any health hazards, what they are chemically. A good rule of thumb is the fewer pigments a color has in it, the more it will "pop" (note: the doesn't apply to things that use "earth" or "soil" as their pigment's proper name like your siennas, umbers, and sepias).

I'd recommend checking out Ian Roberts on YouTube, not gouache specific but his advice on perspective and composition is excellent, not overly technical on cityscapes

I think the magic of gouache is how the layers interact, the colors seem to glow from within. I'd recommend putting down a really saturated, raw underpainting first and get more subtle and mixed as you go.

As far as urban landscapes, in my opinion if you know 1-point perspective pretty well you get away with fudging just about anything. Look for the largest, simplest shapes the light is making and paint those.

I spent 10 years reading books, watching videos, and getting lessons on perspective. I thought i didn't understand it because everything i drew was wonky. One day i suddenly realized, while i was reaching the end of yet another book on perspective which all made sense to me, that my problem wasn't that i didn't understand it--it was that i'd been trying to learn it before doing it. If i'd just drawn one thing from real life each day, even something much less complicated than a building, at the ten year mark i would have been as good as anyone making the books/tutorials/etc.

So that's my advice: make sure you're practicing. I'm still paying for that weirdo mistake, but i've improved TONS since i stopped reading and watching and actually started drawing. ❥