It's kind of hard to say when we don't know your power, the ninja's or summons you have, or which of those ninja's are cultivated. Also, not every mission can be beaten right away. Some missions you HAVE to come back to (Life-Threatening Battle took me months to beat simply because I didn't have the right ninja's or power). Utilize ninja's like GNW Kankuro for his Ignite/Poison, Hinata for accupuncture/defense, and any other ninja's that you c*e for control builds. Make sure to target bigger threats to take them out first. The worst thing is that RNG determines a lot of battles. You can do the same battle 100 times and get different results each time because of things being random. Usually people give a line-up for missions that worked simply because they got lucky. Safest bet is just to be stronger and come back later, otherwise you'll have to post screens of your ninja's and give more info.