after you learn your 2nd language is the 3rd easierWatch
But how 'easy' depends a lot on the language.
For example, if Spanish is your second language, then learning Portuguese is pretty easy as the two are so similar. Whereas knowing Spanish won't be too much help when it comes to studying a language with a totally different vocabulary and grammar, such as Finnish.
However, having learned one language already, you will at least have knowledge of grammatical concepts which will make learning any third language slightly easier. For example, knowing French won't really give you much help with Russian vocabulary or grammar, but at least you'll already be familiar with the concept of grammatical gender. As you say, you'll already have some language learning techniques, so learning verb conjugations etc. will be much the same, even if the differences between the languages are great.