Do them in whatever order you feel like. Many schools insist you have passed air law before you go solo and have passed the navigation before you do solo navigation though so it may be an idea to get these done first. As for RT I have been advised to leave thse till last as you will be fully competent and confident by that point.. .I have only the RT practical left to do now but I reckon I will have done that before I go solo as well. Good luck and dont panic you will be fine.