When I bring a horse back into work I like to bring everything back slowly almost like they are a baby again, since not having a saddle on for a while sometimes it's a bit tender getting used to it again. Just think of it like you used to go to school carry a bag you got used to it, then have a few years off and man that is actually heavier and not as easy as you remembered hehe
So normally start with lunging no extras not even bridle just for 10 mins at the most no canter, do this maybe a few times depending on the horses health, age and prior training. Then next time saddle, then introduce the bridle and if you use an extra aids such as side reins etc you can incorruprate them but becareful reaching for things like this with an unfit horse. I would just normally lunge for a few days, then by day 3 or 4 have a litte ride just walk maybe trot. Once you have got on the horses back and established that they are strong and not sore etc I prefer to bring them into work hacking, keeping in mind their fitness level with times and ammount of work involved then once they seem to be calm and level headed, often bringing a horse back into work even the quietest horse can be a little distracted and not the same horse they were before. So with a little bit of fitness normally comes a brain so about now I would start flat schooling or what ever you may do with your horse.
Seems to be my theme for the day a lot of waffle for a simple answer hehe lunge for a few days, quiet rides till you feel like you have their attention and then proceed as you wish.
Enjoy and you should be fine a horse can easily be brought into show fitness in just a few months if your dedicated just keep the work up