One of the most basic aspects of proper use of object oriented programming is to properly design your classes in the first place.
Designing a Class

Object Oriented Programming languages make developing programs to run on multiple operating systems much easier. All you need is a class library of common functions that has a separate version you can link in for each of the operating systems you want to support where the public interface to the multiple copies of those classes [...]

If you are using a programming language that supports classes then obtaining a class library that supplies a lot of the common functionality that you need will save you a lot of time. Regardless of whether you actually do that or not there will be a whole lot of functionality that your projects will require [...]

One of the big benefits to Object Oriented Programming is being able to define classes that can be reused from one project in another. A class library takes this even further by providing a prewritten set of classes that can be used in all your projects.
What is a Class Library?