Welcome to forum @Animallover1 ! (And welcome to @nancyHar !)
Remember the numbers. Even if a host gets 5 excellent applications, they only need one sitter. You’d expect 80 % decline.
It is about beating the numbers. To beat the numbers, learn what is going on. 
A host would ofc prefer a sitter with THS reviews over a sitter without. So getting THS reviews is important.
A host in a high interest location can be very, very picky and still get loads of sitters. Hosts in less popular areas won’t get so many applicants.
Experienced sitters often want nice locations - and longer sits.
Short sits are less popular. Last minute sits are less popular (full time sitters plan months and up to a year ahead).
To get a sit, that means you will be more likely to get a short sit, a last minute sit, a sit in a less popular area. These sits can still be good sits, by all means! But the competition for them will be lower.
It is often adviced for new sitters to try and do a couple of local, short sits if possible. That would give you a quick way to THS reviews, which is kind of the currency to get sits. For local sits one can also offer to meet up before the sit, which could help when one doesn’t have THS reviews. It will be a gamechanger for you when you have 2-3-4 reviews.
I don’t know what your preferred areas are, but for instance UK has so many more sits than sitters (apart from London, which is high in demand for sitters).
But it is all about a good match, and all of us have been new at some point. Read up on forum, lots of great information! Just remember that we are more likely to come here to vent than to share wonderful experiences.
I’ve had only great sits, I think for a large part because I am picky in what to apply for. A good sit is a sit that you too have criterias for. Best of luck!