As someone that experienced DDoS which made whole leaseweb feel it (site i was operating was on servers in leaseweb), I can tell you one thing.. Unless you are

As someone that experienced DDoS which made whole leaseweb feel it (site i was operating was on servers in leaseweb), I can tell you one thing.. Unless you are ddosed by someone from their home connection or one server you need professional DDOS protection. No guide will help you here, you probably don't have the pipe big enough in case of UDP flood and don't have enough resources in case of sophisticated TCP attacks. If you only want to protect your website then go for cloudflare pro, it will be enough for 95% of ddosers. If cloudflare is not enough then you need thousands or ten of thousands of dollars to get protection.