I'm trying to gain weight but I want it to be useful muscle, not fat or bulk muscle, any tips?

I'm 6 foot 5 inches and currently 150 pounds. I would like to get up to 180 at least, but I don't want it to be fat or useless bulk. Does anyone out there have any hints or ideas as to how I can put on some genuinely useful muscle?
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Please don't use the word diet. I share the opinion of Garfield that the word 'diet' is 'die' with a 't'. Just thought I'd let you guys know.
I'm trying to gain weight but I want it to be useful muscle, not fat or bulk muscle, any tips?
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