Is your tank cycled already?
You should add a few more of the same tetras to make a school. Most small tropicals will do alright. Barbs, rasboras, platies, swordtails, rainbowfish. You might also consider a small bottom level fish like a bristlenose pleco or a small group of loaches or cories.
Mixed fruit tetras are dipped in chemicals to get the colors. The process is very painful and the colors fade away with time. Don't give stores money for doing that.