Hi Radiohead, welcome to the forum.
First, posting some samples wouldn't hurt
It's not just about submitting, but about getting listed, getting traffic, and making the most with that traffic.
You need to submit daily, never autosubmit, don't miss a day, build traffic and a reputation. Reputation is important as reviewers will start remembering your galleries and who you are.
Apply for partner accounts. While there's a lot of paid partner accounts now, I wouldn't recommend going that route until you have some experience under your belt. Still, with that said there are a lot of tgps still out there that give free partner accounts away. Having a partner account will get you listed more often, will get you higher on the page, and you stand a better chance of getting into the "sweet" spot of the tgp...the top 1/3rd of the page if you have a partner account.
When applying for partner accounts make sure that you submit 3 unique looking samples, don't use sponsor graphics (headers, footers, or ripped fhg), try not to use overused sponsors, make sure you follow all the rules, make sure you don't use a subdomain, make sure your domains aren't estdomains (as that will get you rejected instantly at most places), and basically put your best foot forward. Also it doesn't hurt posting on forums like this and a few others just so people "know" who you are...it makes it easier to request a partner account.
The sponsors you pick for tgps are very important. If you pick a saturated sponsor your conversion ratio will be considerably lower. If there's 100 webmasters all promoting the same sponsor, using the same sponsor content, etc, you'll soon find that the chance of getting listed greatly decreases and even if you do get listed you're competing against a lot of webmasters going after the same piece of the pie. Research, ask around, know which sponsors are saturated in the tgp market.
Niches, some niches work better than others on tgp traffic. Again, this is a thing you'll have to learn through trial and error.
Don't limit yourself just to TGPs. TGPs are great, you can make a very very nice profit off of them, but they shouldn't be the only thing you're focused on. The tgp market is harder for new webmasters to enter into at the moment, it isn't like it used to be, and you'll need to work even harder to make inroads. You should also focus on building Freesites, SEO them, and submitting to LLs. You should build SEO pages, hubs, blogs, toplists, etc, etc, etc. The key thing is to do as much as you can each day, build each day, and soon you'll see a steady stream of income coming in.
If you post some samples I'm sure the good people of this forum will be glad to help you along
Also, build freesites and post for reviews here and listen to the advice that's given to you.
Good Luck
