Try focusing on your breath, and disregard your thoughts instead of trying to actively block them. (This is some kind of Buddhist meditation whose name I can't remember.) It took some practice at first, but it usually (not always, for some reason) works for me. (Another idea I read somewhere is counting your breaths, but after a while I practised that , I was able to count and think about something else at the same time.)
Fast track to pure focus
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That hasn't stopped a vibrant community of DIY tDCS enthusiasts from springing up. Their online forums are full of accounts of their home-made experiments, including hair-curling descriptions of blunders that, in one case, left someone temporarily blind.