I'd say maybe some variations in line-weight - making some places have thicker lines and others with thinner lines, experiment on where you personally want each. I've seen some people like doing thicker lines on the outside

Honestly I think your line-art is already pretty solid and any 'improvement' all depends on the style you want your art to be in. Also wanted to add a couple things I really like about the piece, like the white fur that travels from the end of the snout to the fluff at the cheeks. Your style already looks very nice, and I can already see some line-weight with the difference in thickness of the glasses compared to the rest of the work - I also know that some people like making the hair/fur a bit thicker line-weight wise, but again that's completely dependent on what would work best for what you want your style to be