Not all brokers are created equal. Some are much better than others in certain areas. That’s important to remember, because “in certain areas” does not mean “in all areas.” This makes your job tough, since you do not have the same expertise and needs as other traders do. So, a site that specializes in 60 second Forex options will not benefit you if you are looking for month long index options. Also, some sites are better for traders with a lot of money, while others focus on their clients with smaller accounts. Simply put, if you are going to trade, you need to define what you are looking for clearly, and then go out and find the brokerage site that best fits those needs. 24option, Traderush or Redwood Options may be your best place to start. It can be time consuming, unfortunately, but there are many resources on the web that will help you to narrow your search and find the perfect site for you. Other sites like binarydealer.com will also give you enough broker reviews to help pick the right site. You really have endless places of good information.
First, establish the percentage of your trading capital you are willing to risk on a single trade. Ideally, this should be 1% or 2%, with the absolute maximum being 5% (not recommended). For a normal binary options trade, this dollar amount gives you your maximum position size. For a Nadex option, also consider your maximum risk on the trade, and then calculate how many contracts you can take to stay within your risk limit.