Without taking a good look at the other teams in your league, you should be able to promote next season or the season after if you develop a strong understanding of the game (like enthusiasm, game shape, etc.). There are people here that can help with that (and the fact that Jason has already pitched in is big . .. he is a great resource).
I HIGHLY recommend you get a level 4 or 5 trainer, but then spend cash ONLY on getting your arena much larger. Cash is a huge factor in being successful at the D.IV level and higher . . . and you need to start building your arena for that now. I am a fan of lots of smaller improvements (adding 500 bleachers 4 times during the season rather than a 1 time purchase of 2000) since the larger purchases take so long, but some people disagree. I believe your goal should be to have around 8000-9000 seats when you promote. Get to 6500 bleachers as quickly as you can (since you will win most of your games next season - and winning is the key to fillnig bleachers).