I guess I need to be patient with this machine.
I know this is an older thread but this holds true for most sergers... patience is key, and if you do end up frustrated with something, it's usually best to take a break rather than force it.
I have two relatively high-end sergers (a Pfaff 4874 and a BabyLock Imagine) and the Pfaff is VERY picky about the "order" in which it is threaded. It has to be upper looper then lower looper (which is counter intuitive, as it would seem to make more sense to thread everything from right to left), or it simply will not form stitches correctly (usually it breaks one of the looper threads, forcing you to start over, but if you're doing it wrong, it just creates a nasty cycle). The Babylock doesn't have that problem (but it has air-jet threading, which you can only use with the loopers in a specific position, so it kind of prevents it by not allowing you to thread it in a different position).
A caution about using "stretch" needles in your serger, some are quite picky about needle type... make sure you don't need to be using a special needle before opting to try a generic stretch needle. My Pfaff needs specific needles for coverstitching or it will skip stitches.
Another suggestion I have is to take the scraps leftover from cutting out your pattern, and test the actual fabrics to make sure your threads/tension/etc will work well for a given fabric. I often have to make adjustments, particularly on the Pfaff (which I mostly use for coverstitching) It's always best to double check rather than guess
If you are shopping for a different machine, I can also recommend the Brother 1034D - I had one for many years, and I sold it when I bought to a machine that did coverstitching (thinking I didn't need two sergers). It only took me a few months to regret selling it, at which point I went in search of a second serger, which is how I ended up with my Imagine - it was well out of my price range (so was my pfaff but I got a really good deal on it) but after sitting down at it I knew I had to have it.