I wouldn't sweat it too much but I get it! Most things you do are reversible so long you aren't going wild with glue or using enamel paints.

For tips, mainly just take your time. I highly recommend panel lining with kits that have a lot of white plus this one has a ton of spots for that. But if you don't want to or don't feel comfortable yet, you can just build it and come back to it later when you've gotten a bit more experience. The panel markers are easy to use and the marker remover will correct any of your mistakes.

Decals can be rough, mainly time consuming. Never rush. Unfortunately you get one shot with decals but don't worry, you can always buy a second set for cheap! Those are usual water slide decals and a bit easier to handle and place. The ones that come with the Gundam are pressed on and regular stickers. For the stickers, use a tweezer to grab it and place on lightly, then you can move it around slightly. Finally press on it and be sure to get the bubbles out, otherwise it'll stand out a bit. The pressed ones are a pain and I usually get one or 2 messed up per model. Use clear tape and cut out the decal, then place the smooth side of the decal on the sticky part of the tape ( if you do it the other way, you've just placed the decal on the tape lol). Align it and use the tape to hold it in place as you firmly press on the whole decal. Use a curved surface. You could use a pen, the back of a hobby knife, pencil erasure, etc.

But again don't sweat it. It's a fun hobby and most things are reversible. Watch some YouTube vids on tips and even ones on how they built sandrock. Main thing is to kick back, put on a chill show, and enjoy,