First of all, talk to Seth in the entrance of Shady Sands and talk about the Raiders, with marks the location of raiders on your map. Second, talk to Ian, first house to the right and talk about both Junktown and The Hub, both location will be put under your map.
Now, if you did not completed the Rad Scorpions quest, do it now, either by killing everyone there ou putting a bomb in the weak part of the cave with a dynamite that you encounter in Vault 15 (I kill almost every scorpion, then blow the entrance, just for the XP), and if possible, take at least 1 radscorpion tail, so that Razlo can make a cure, and then you can cure the poisoned guy in the room in Razlo house, grants you 400 XP and some good karma Also, before the Scorpions quest, it would be good to take Ian to your party, since he is a killing machine and helps a lot.
Now you can go the Raiders camp and maybe do the quest for the leader. It will grant you -4 points of Karma, put is a really easy quest and grants you 500 XP, besides these -4 points are nothing, since good karma is not hard to get. Also, one thing that I recommend is to steal the Raiders, not everything they have, but just the Stimpacks, Drugs (including the drinks) and the Molotovs, and if possible get the Grenade and the magazine that is located close to the bathroom. You can kill the Raiders, but I sugest not yet.
Go to Shady Sands, talk to Seth. If he talks about Tandi and how she got taken by Raiders, then it means that you got another quest to do. If not, wait some days and go back until you got this dialog from him. Also, if you got this dialog, you can talk to Aradesh for more information and a free Spear.
Go to the Raiders Camp, talks to the leader. You can convice him to let her go if you have enough speech, buy her or kill all Raiders to free her (dont recommend the letter, since the raiders start attacking Tandi and she dies very easily, so be careful if you do decide to take out the Raiders). Also, if you do kill the Raiders, use Psycho and at least 1 Buffout, it helps becuse of the damage, oh and take their loot (especially their armor).
After that, take Tandi to Shady Sands, and you get a nice ton of XP.
After that, go to Junktown and continue your journey, and good luck.