I am not an expert, but I will try. Here is your last game. A big part of avoiding tactics is learning how to avoid positions that allow tactics to develop. See the notes in this game which was your last loss. There were a lot of positional mistakes that make you vulerable to simple tactics. Also, in preparation for your 19th move, you needed to really calculate hard before you make your move. Spend 5 minutes if you have to because there was a lot going on. One final point to make regarding avoiding tactics. When playing chess, our brains get tired. When they get tired, they make mistakes so be mindful of positions that require a large calculation load.
You might want to take a pawn, but if that pawn opens up the position and allows a lot of potential for your opponent, at the very least, your calculation load will go up. I am playing a 3day online game where I am up an exchange and I decided to grab an en prise king side pawn to ensure the endgame win. I was thinking this has to be good because it wins a pawn and opens up the kingside, exposing his king. This did in fact ensure the endgame win, yes, but it also opened up the g-file for his rook and queen. The tactics this opened up were unbelievable. I trully would have lost this game if it weren't for the fact that in on-line chess you have access to an analysis board and plenty of time to calculate. I've never calculated so much in all my chess playing, just to survive the game. So be mindful of moves that give your opponent a lot of activity. They might be good moves, but you also have to think practically about what your brain can handle.
Another way to avoid blunders is to make the move in your head and then visualize the position in your mind for about 15 to 20 seconds (don't make any additional moves in your mind while you take the time to do this). Once you have that position "fixed" in your mind, take a look at what moves your opponent has. Move everyone of his pieces in your mind if you have to. To "see" the blunder, you might need more time to fix the position in your mind. Obviously, you don't want to do this on every move, but when there is a lot going on in the position like moves 18-20 in this game.
One final point I want to make is that it is clear from this game that you should be calculating more lines. Whenever you find a line that you think is promising, stop and look for a better move. You'd be amazed at what you will find.
I have lost a lot of games lately due to silly tactics. It's not because I don't check for tactics- I do. It's a part of my checklist. I find that I just don't see tactics because I overlook moves. In other words, my tactical skill is really bad, and I don't think tactics trainer is helping. In tactics trainer, I know that I'm looking for tactics, so I just look at every forcing move. In a game, positions like that don't come up all the time. Besides, I don't learn from tactics trainer anything other than the moves, even when I do it slowly.
So is there any way to improve at seeing chess tactics that has worked for anyone out there? I am grateful to those who answer. The things I miss are not combinations, it's just often things like bishops pinning my rooks to my queen, missing outside-the box moves that wouldn't immediately be obvious that win material, or forks in the middle of the board.
Also, I am playing in a chess tournament soon and I fear very much that I will lose in this fashion in my tournament due to tactics. Is there anything I can do in the next few days that will help me see this stuff?