I am a long time combo knitter --
when working anything with purls, (flat or in the round) you have to adjust. (most often, when working in the round, there are fewer purls.. if working in stocking knit, (KNITS) only, you find your stitches will be mounted (sitting on the needles conventionally) and you can follow directions as they are written.
but when working flat (stocking knit especially) you'll have to THINK about the decreases.
here's a memory trick--a number 2 has a /in it..
and a k2tog results in a decrease that leans to right / just like the number 2
and a SSK or S1, k1, psso --has an S and inside the S is a \ left leaning slant.
so.. if you the pattern calls for a K2tog the pattern is calling for a / Right leaning decrease
and if the pattern calls for a SSK or S1,K1, psso, the pattern is calling for a \ left leaning decrease.
as a combo knitter, you'll need to reverse the decreases.. but you'll be able to understand (and create) the correct decrease by looking at your work, and remembering which kind of slant is desired--