make sure to prepare your fabric for dyeing or use prepared for dyeing (pfd) fabrics or the ready made printer fabric sheets. let the ink (cure) completely dry then heat set. on the prepared sheets follow the instuctions. i always let mine set for at least 24 hours after running through the printer before i heat set it. i use an HP printer and always make sure i have new HP ink cartridges when i start a fabric printing project. (the inks in the 'refill' off brand cartridges is not dependable it washes out, fades, runs...ruins) most of the comparisons i've read say to use HP or Epson ink jet printers for the best long-term results.
it is wonderful to start experimenting with printing fabrics, have fun with it, just make sure to wash the sizing out of your fabrics. and white fabric is going to give more vibrant colors than natural muslin.