Since OP has already read “Guards! Guards!” by Terry Pratchett, I instead want to recommend
“Men at Arms” by Terry Pratchett, the direct sequel to “Guards! Guards!”.
And again, as it’s so handy to find your way around the Discworld, this chart shows how the books relate to each other.







If I were you, I would really continue with the Watch series, it has some great characters and storylines, and it will make you fall in love with the Discworld universe.
Once you have either read all the watch books, or feel like you need something different, then I would probably try out the Witches series. (or possibly the “Death” series, eventhough the first book “Mort” is a bit rough.
And only then would I circle back and take on the Rincewind series. The Rincewind series starts out rather rough, compared to most of the other books (but they were also the first), and there’s a number of details and characters that are not consistent with the rest of the books as Terry Pratchett was still figuring things out at that point, and while the Rincewind series becomes very very enjoyable as it develops, I will say that the first two books are a bit harder to get into than the rest of the Discworld series.