If you are looking for real cheap and easy.....
De-grease and clean the frame all over with washing up liquid and warm water, a sponge scourer from under the sink will suffice. rinse thoroughly with plenty of water.
Once totally dry apply clear lacquer(rattle can) available from motorists' shops/DIY etc... follow steps on can and that should be that. the existing paintwork will be even duller and will help provide a key for lacquer to adhere to.
This will cover up more imperfections than you think and help get more riding out of your bike knowing it will stand up to weather/mud better. This will set you back less than a tenner. Of course, before the pro's step in, this isn't a process intended to be bullet proof or conform with xyz of the paintwork ideology. but, it does work on a budget
Just make sure you scrub frame well as left over greasy spots will show in lacquer as icing sugar.
Ride yorkshire on an old bike.