Every design can really be different, with stitch pulling effects on the fabric possibly exacerbated by the design, characteristics of the thread twist and quality, etc. For each one, really, it can take some testing, including varying some or all of the following:

FABRIC

• I always use scrap fabric that's exactly like where I'm headed. If I'm doing t-shirts and it's a new kind of material to what I'm used to, I'll relegate one t-shirt to be my practice one and it will get 20 trials all over it. If I’m lucky sometimes, I’ll only need one shirt.

STABILIZER

• one sheet or two? or more?
• tear-away, cut-away?
• lightweight? heavyweight?
• use more sheets of lightweight instead of one heavyweight?
• would sticky stabilizer work better?
• use above as well as below?
• if you're using sticky stabilizer, is the adhesive sticking to the needle and impeding its progress?

THREAD

• if it’s breaking, try a different brand. I cannot use one brand of embroidery thread on my home embroidery machine but someone else at TechShop can use the same brand on the TechShop embroidery machine and we have the same machine. I cannot explain this. All I know is that after discovering this, I've accidentally grabbed the wrong thread and used it and it has broken as before.

NEEDLE

• is it sharp enough? some people swear by this. I honestly use needles for a long time without troubles. When I start having stitch/hoop problems, I will swap out the needle to see if that's the problem. if you're using an 11, try a 13, or vice versa. I wouldn't typically use any other sizes on that machine. maybe maybe a 9 but not any larger than 13.
• is it bent? always want to replace a bent needle with a new straight one.

MACHINE SETTINGS

• maybe slow the machine down from 650 stitches per minute to 400 spm.

MACHINE STATE

• is there is a stray piece of thread somewhere in the machine? try checking the thread path through the top and also take out the bobbin and look around the base for any stray thread or bunch of fuzz/dust and gently brush it out.
• is the thread able to easily come off the spool on top? sometimes the thread catches on something (usually the spindle that's holding the thread spool) and it makes the thread tight, leading to it breaking.

DESIGN

• too many layers causing thread to break?
• stitches too dense?
• does thread pattern fit the shape?
• are you using satin stitch for too narrow or wide of a design?
• Something I'm currently working on has required a lot of rework in this regard. You may want to look into creating a background and then creating the smaller shapes (letters?) on top of that and then experiment with different stitches to get a good look. Two layers should not break the thread.