If you had a temporary residency card in Spain (i.e., a card for one or two years), after the beforementioned 3 years you will be able to return to the country but for this, you will have to start your application from 0.
That is to say, you will need to request your initial residence authorization from the beginning (you cannot renew the one you previously held or go through any similar procedure that is based on your prior residency).
The most common case is to apply for an initial residence and work authorization as an employee.
That is because this voluntary return has one main benefit: you acquire preferential processing for your immigration application.
In addition, the national situation of unemployment in Spain won’t be taken into account. That is to say, even if there are Spanish nationals who are unemployed and also want to apply for the same job position as you, this will not influence your capacity to apply for that particular position.
This whole process will be carried out from your country of origin, starting with finding a job offer (a company that wants to hire you), and then it will be your employer who will start with all the paperwrok first.
The rest of the general requirements to apply for your residence permit must be fulfilled as usual. That is to say, if you are going to apply for a non-lucrative visa, for example, the requirements are the same for this residence as if you were entering Spain for the first time.
