For improving website’s seo, first improve its on page seo, on page seo should be perfect and foremost step towards a strong seo.
and website should have https do not use http for the website.
Content is king always so make sure website have high quality and unique content and pages are interlinked with each other.
Website should be mobile friendly and fast loading speed.
Focus on above things then start link building and remember quality is important then quantity, so make only good backlinks.
Track your competitors progress, check on which keywords they are ranking. Track competitors backlinks.