Now a day , website is essential need for any business. if website is good respect to design and UI. than it can earn million customers.
before to start the design part of any website . you should check some point with your designer.
Define Your Audience
First of all define your Audience / Client / End Users from who you designing website. you need to research little bit what their like/dislike , which aged group people gonna use it so you can choose best suited color scheme , design UI , related icons , related graphics.
suppose you are designing the site for school which for younger age group , you can choose font as "Luckiest Guy" ,if for teenager choose try to make funky theme.
Plan The UI first.
Dont start direct to design but first plan the UI.
suppose you designing the mobile app. try to make UI at aviliable tool for prototyping
Creative UI is the key to attract more customers.
Try to make better and creative UI , with best text animation and better User Friendly Forms.
some time when i filling some registeration form at some website is like answering question paper in exam. try to ask as little info at first step at registration,like name , email , password thats enough for first step.
Use Open source and freely aviliable jQuery Plugin , Angular plugin to make site friendly to users.
Use Flash (dont afraid from SEO Guys).
Use Flash when you needed , leave SEO aside for a minute
Mostly designer knows that Search Enginee dont read Flash so mostly they try to skip the FLASH . yes you are right but when its needed or better to experss in FLASH than choose it . dont worry about the SEO part because good User Interface pay you back.
Same stories come with Ajax . Mostly Ajax loaded data will not go good with Search enginee but it give more comfort to user than better to use it