Ah the pre reform house of commons.

As always the answer is it depends which ones.

Essentially you had 2 main forms of MPs. The knights of the shires that represented counties and those that represented urban centres. Then you had varies other MPs such as those that represented the Cinque Ports (University constituencies though cam rather later.

Now we've got that out of the way it depends on the date. 1430 is a critical year as is when the 40 shilling freeholders act was passed. After that date you needed to have a freehold worth 40 shillings a year in rent in order to vote in county elections (prior to that point is possible that all freeholders had the vote in theory). One big catch was that you had to vote in the county court. This meant if you didn't live near it voting wouldn't be very practical. An exception was Hampshire where you could vote in Newport on the Isle of Wight as well as Winchester. Voting was public so you might want to stick to candidates that the great and good of Winchester were happy with. So in practice such MPs were selected by who met the voting requirements, were able to get to the county town and were prepared to openly support them.

For MPs that represented towns the system was largely left up to the authorities of the town in question and a range of approaches were taken from giving the vote to most householders through just those that paid certain taxes to just the members of the borough corporation.

Of course this assumes that any MP was chosen at all. Southampton for example repeatedly failed to provide an MP (at the time it was expected to produce two). This makes more sense when you realise that Southampton was frequently a poor town and parliaments could be held in some fairly random places.