there are a couple of different ways. For me I just cut up fresh fruits and vegetables.Like apples and Carrots I use a peeler and slice it thin. Some people take all the fruits and veggies and put them in a blender, pour them in ice cube trays and freeze them. There is also dry gutload such as Cricket crack that can be purchased(I think TikiTiki Reptiles sells It) and it is full of good nutritional stuff and the crickets love it! I am sure there are other ways but these are just a few!
I gutload each morning (may be a bit obsessive) 3-4 hours before feeding. I change food everyday I use Carrots, Kale, collards, strawberries, sweet potato, apples, oranges (all fresh of course) and switch them up I do not add all of these ingredients everyday. Place them with your feeders. I normally empty the cricket keeper tubes and raise them so that all the crickets can chow down. them drop them back down by hour 2 or 3. Also use the Cricket crack so to speak, hydration by flukers. Make sure you dust with regular calcium as well (the feeders of course when ready to distribute to your cham).
Her blog in general is one I've used several times when I needed information about gutloading and such. There's also recipes for dry gutload and some "Bug Bread" somewhere in there. I've been using the bug bread for Crickets and Supers. They both eat it.
Usually I offer an appropriate fruit or vegetable, and some bug bread or dry gutload. Sometimes I put in the Fluker's hydration cubes or I soak the bug bread with some orange juice. Sounds like a lot but I only keep small amounts of crickets at any given time at this point so I usually just stick a small piece of the bread in and a slice of orange or a few leaves/pieces of whatever veggie. Remove uneaten food after 24-36 hours.