Speaking English certainly makes it easier to speak German than if you for instance only speak Japanese.

There a couple of features that German shares with English:
- the existence of determined and undetermined articles (though in German you distinguish by gender)
- the use of prepositions
- the tenses are formed rather similarly
- many words have the same origin and hence are written and pronounced similarly (intelligent, warm,...)

There are also quite a bunch of differences:
- German has three genders (male, female, neuter) for nouns and you really have to know them, even in practice. Knowing French, Italien, Spanish or Dutch (just as an example) might help you in this respect since these languages also have this concept although the assigment might be different in individual cases. French has no neuter for instance and the gender for moon (der Mond, la lune) and sun (die Sonne, le soleil) is just the opposite.
- the pronouncation is of course different in many cases (and maybe more logical for German)

I don't have any clue about Turkish but knowing English will certainly help you with the German vocabulary, especially if you are heading towards "more intellectual" words of latin origin.