Ways to promote business?

Me and my partner sell branded goods for mobile phones (tempered glass screen protectors, cases etc.). We sell most of our stock through Amazon unfortunately, but we have started to sell more on our website now possibly due to the SEO kicking in.

We do advertise through facebook and twitter, but we were wondering if there were other avenues we havent thought of.

We also want to start promoting in the outside world, and sell to retailers but we have no idea where to start, any advice would be majorly appreciated!

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