Experience shows that while some people can get away with just new fuel and a carb clean, most of the time there are other things that need to be at least looked at. I guess it depends on what you want to do with the bike, how much cash you want to spend on it and how prepared you are for it to, quite literally, go bang.
Where applicable, timing, plug, points, filter, carb etc will all have an effect but without knowing if the seals and compression are right you may never get the bike to run correctly and risk damaging parts which will cost you additional money.
A lot of old bikes have been bodged (made to work using more Heath Robinson innovation than technical expertise). Investigating and confirming what should be on the bike is the start. There are lots of experts here who can help. Next is how deep you want to go, and when. I recently rode 200 miles on an engine whose history is still an unknown. It ran like a pig but did get me there and back. I have also used it in the same condition to take me to work and back. A 42 mile round trip. It still runs like a pig, even with a new carb from a good friend on the forum.
The engine I have mentioned is my spare engine, the original is stripped. This is going to be rebuilt over the winter and that will then give me the confidence that certain parts are OK and if there are issues, they must be elsewhere. Stripping the original engine has already flagged up that both 5th gear cogs (Drive and driven) need replacing. Obviously the engine will be fitted with all new bearings and seals on the rebuild.
Good luck.