Perks are a collection of bonuses for a character or for the entire party, which you buy in the course of gaining experience. These characteristics can be divided into common, that are available for all the characters, and ones that require development of a certain perk. Diamond symbols on bars signify at which level a characteristic can be bought.
Perks have been divided into strings and stand-alone. The former need to be bought in accordance with a predefined order. Without buying the previous one, you will not be able to get the successive ones. The latter can be bought regardless of the rest of them. In other words, if you want to buy desperado for pistols, you will first have to reach a certain experience level and buy the bandit perk. Meanwhile, the focused perk can be bought right after you achieve the specific experience level.
Each character receives 1-4 character points, every 4 levels (4, 8, 12 etc.) and they can be spent at any moment. Therefore, you can buy a certain attribute immediately, or later on, when the array of the available ones expands. Thanks to this, you can hoard points until something better appears, which may never happen, as a matter of fact. Character development is a long process, especially if the character is low on intelligence and as a result, the available attributes will not be plentiful. For this reason, it is best to buy characteristics as quickly as possible . Unless the perk that is important to you becomes available at the next experience level, in which case it is better to wait.
While selecting your perks, start with the ones that require certain perks, and then take interest in the common ones. The latter ones can be picked by just any character, usually one or two per party. Of course, not all of the perk that require you to develop your character are attention-worthy, but they still should be your priority as specialist ones. Apart from that, buy perks in accordance with your needs, because the majority of them prove to be useful, sooner or later.