Use extra tags in your description. This in my experience helps quite a lot in rankings.

To find extra tags go to http://keywordtool.io/youtube (youtube is being a bitch and has disabled their keyword tool) and search for the niche of your video. For example, if you search 'Far Cry 4 download', click Copy All and you will write something like this in description:
Extra tags (please ignore):
far cry 4 download pc,
far cry 4 download utorrent,
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far cry 4 download free,
far cry 4 download and install,
far cry 4 download mega,
far cry 4 download mac,
far cry 4 downloadable content,
far cry 4 download ps4,
far cry 4 download skidrow,
far cry 4 download pc,
far cry 4 download utorrent,
far cry 4 download pc free,
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far cry 4 download and install,
far cry 4 download mega,
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far cry 4 download ps4,
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far cry 4 download xbox,
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far cry 4 download crack,
far cry 4 download demo,
far cry 4 download free,
far cry 4 download free pc,
far cry 4 download for pc,
far cry 4 download full version,
far cry 4 download,
far cry 4 download pc,
far cry 4 download utorrent,
far cry 4 download pc free,
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far cry 4 download and install,
far cry 4 download mega,
far cry 4 download mac,
far cry 4 downloadable content,
far cry 4 download ps4,
far cry 4 download ita,
far cry 4 download key,
far cry 4 download link,
far cry 4 download mega,
far cry 4 download mac,
far cry 4 download maps,
far cry 4 download pc,
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far cry 4 download ps4,
far cry 4 download ps3,
far cry 4 download pc repack,
far cry 4 download pc ita,
far cry 4 download pc mega,
far cry 4 download pc nosteam,
far cry 4 download pc and install,
far cry 4 download pc skidrow,
far cry 4 download rip,
far cry 4 download skidrow,
far cry 4 download tpb,
far cry 4 download torent pc,
far cry 4 download thai,
far cry 4 download utorrent,
far cry 4 download with multiplayer,
far cry 4 download xbox,
far cry 4 download xbox 360
Just remove the commas and get ready to rank!