Bitcoin proposals are sent out to interested parties and published publicly. The voting on whether a proposal is good for the community comes down to all involved participants, but more specifically the miners and mining pool operators as they carry the full node and are therefore capable of refusing to participate.
The method used for voting is where each miner includes a piece of code in their coinbase transaction (i.e. when they win the proof of work challenge) between a specific time set by the developers for the vote on that particular BIPS proposal.
The vote could take place over let’s say 100 blocks, in which time a mining pool will include its yes or no vote in the blockchain 30 times of it controls 30% of the hashing power, so votes are proportional to the percentage of hashing power attributed to the network.
So the process is that developers make a proposal and then miners vote on it. If there is a majority vote for yes then the code is implemented by the miners. A majority is defined as when over 55% of the miners vote for a specific change.
This mode has led to some criticism in 2015 as devlopers have vied over the future direction of Bitcoin itself. With miners voting against various proposals that are not in their interest but potentially in the interest of other parties. As the blocksize becomes insufficient, miners could benefit from elevated fees as space in the next block becomes highly sought after. In this manner the voting proposal of BIPS can be governed in the interest of particular industry participants and not the network as a whole.