Any good tips for tie dying?

i tie dyed for the first time yesterday. i used a kit which may or may not have been not the best way to do it. im not disappointed with the way the shirts came out but the colors are not vibrant. i like bright, bold colors and i dont know what to do differently next time. any tips?

also, i rinsed them about 14 hours after dying them. the kit said the longer you left them sit, the deeper the colors would be. it suggested 8 hours. i rinsed them in cold water last night and then washed them today real quick. maybe some of that has something to do with it?