While I don't have much ATOW experience yet I have been running games various rpg's for about 28 years so here's some generic advice...
Don't be tempted to over-power the character to compensate. In ATOW terms don't grant more XP at creation. Typically this does nothing to overcome the major weakness of a one person party (no back-up) and means your bad guys have to be tougher reducing the referees margin for error to razor thin.
Do encourage a PC concept with broad capabilities. For example for ATOW don't create a skilled MechWarrior with and Assualt Mech, instead if you really must play a mechwarrior go for a light mech and use the saved xp to build a noble/pollitical background or some time as a secret agent or as a wilderness hunter. You get the idea.
Do provide an employer organisation. The employer provides direction when the player/PC faulters in driving the story. Also an employer can provide NPC back-up, gear, medevac or whatever is reasonable within the scope of the story.
Cut-scenes: If an NPC the PC cares about is in trouble give the player control of the NPC for the scene even if the PC is not present. Be sure to instruct the player to stay 'in-character' for that NPC.
Adventure in a civilised place. In a Jihad style total warfare battleground any single PC is gonna die quick. Consider instead peacekeeping in a recently 'liberated' planet or spying within the palace on New Avalon. Where the rule of law applies and communication is good baddies must consider the consequences of being charged with murder, they might try to blackmail or hold hostage rather than kill, muggers rob but don't stop to slit throats after etc. Also the PC can call her employer or the authorities for help.
Help has consequences and is limited. A med-evac takes 1d6x10min to arrive, too many calls for help and you miss out on promotion, the cops want to ask questions you don't want to answer etc.
Injure the PC. When the PC messed up don't fail to inflict logical consequences. Not just wounds, try debt, loss of face, loss of prized gear etc. There has to be a feeling of consequences to failure or the tale becomes hollow.
Kill the PC. Yep. having said all of the above the entertainment of rpg is greatly diminished if the player believes her PC is never at risk. I recomend about once every five hours of play there should be some obsticle that could end the game (a firefight, an even mech battle, a murder investigation, etc)