The best way to have a successful start up is to be honest with yourself. These are a number of core problems that will stop an idea becoming a strong product.

Brutally validate your idea - it's probably been done already. If your only USP is "we'll have better UX", the chancers are, you won't. Does it have a solid revenue model? Ad revenue is no longer a viable model for new product. If you are not addressing a commercially viable unmet need, then you are going to struggle. People are keen to tell you why your startup is a terrible idea, but that doesn't mean there isn't an idea around the similar area.
Don't outsource a cheap proof of concept - This i the number one mistake I see from a technical point of view. Outsource proof-of-concepts are generally terrible, and the first hires will be spending most of their time taming this code base. It is often a situation where more requirements have emerged, and would be more time efficient to start again with a fresh build. Giving serious consideration to completely starting again. This cannot be overstated. One really good developer is so much better than a whole team of cheap devs.
What skills are missing? - it's really important to be clear about where there is a lack of skills (usually product), and what steps are being taken to acquire those skills. Founders usually take responsibility for product, yet they typically have no experience of it. Think of a music fan trying to write a piece of music despite having no experience of music, but they "know what they like!". A good reading list and YouTube playlist will help. You can never overlearn product.
Build a solid product roadmap - use an existing frame work, such as RICE, to rank the top level features of your product. This should give a view of the next 3 months worth of work at any time.
A convincing demo - a solid demo deck.

Check list

A strong idea that stand ups.
One strong engineer to build the prototype.
Allocate time each week to product.
A roadmap.
The pitch deck.
Runway for 12 months.