If you are using a HFT bot, you need to find a low spread instrument. It can be done during a controlled volatile momentum (direction is “persistent”). For example to what happened to XAU last Friday. .It mostly happened after a big impact news.
Next thing, you must check your terminal latency. For target below 5 pips, latency must be 25 ms or faster, even sometime slippage may occurs and got zero or minus. Even you have an ideal environment, you need to know that you are served together with other client. So your order will be put into order execution’s pool.
For example, if you are using ICMarket, your need a VPS near their server, which is New York. If possible, find a VPS provider that has the same data center with IC Markets. New York City Server is one of the example.
The ideal environment for HFT will be a dedicated MT4/5 server. It’s unlikely to be happened for us as a retail trader. But I did it before for an trading firm. The other option is look for new broker which hasn’t have a lot client. Usually a new white label broker. But once the broker has more clients, you will face the same problem again and again