When mixing is new to you, you probably don't own a lot of expensive equipment. A good pair of monitors are most likely to be pretty expensive but in my opinion one of the things you really should prioritise to spend your money on. To be a good mix-engineer you need to hear what you are doing, that's why you should get yourself a good pair of monitors and also a good sounding room to mix in. If you don't have a pair of monitors and still are mixing with headphones consider these points...
Using Headphones Instead Of Speakers
The biggest difference when you are working with headphones instead of speakers is that the left headphone driver is just playing to your left ear and the right headphone driver is playing to your right ear. When you are working with monitors the left speaker will play to your left ear and wrap around your head into your right ear (with a bit of delay). This will cause an imaging that doesn't exist with headphones. Also when you pan things hard left or hard right it will sound obliquely unless you have something on the other side to balance it up with.
How To Get The Most Of The Situation
Buy a pair of open air headphones. These headphones are vented on the backside and let the driver to be more efficient and doesn’t lock up and build up the low/low-mid frequencies which will lead to bad decisions when mixing. Of course these headphones are pretty useless for recording because of the leakage. So you probably want to get a pair of closed back for recording situations.
There Is A Plugin That Can Help
If you are mixing a lot with headphones you consider getting yourself a copy of the Redline monitor plugin. This plugin is designed to make your listening experience more natural. It allows you to feed a bit of the left side driver to the right side driver with a bit of delay to simulate how things should sound when mixing with a pair of speakers. I believe that there are a tons of these kind of plugins on the market, but I have just tried the Redline monitor and it works fine. I am not saying that this plugin can replace a pair of monitor speakers but it could be great if you don't have the ability to check your mix with speakers at that moment.
The key issue is to listen. Listen to your favourite tracks and the Billboard charts. How does it sound in your headphones? When you are feeling confident with your headphones, you will most likely do good mixes. And remember, even if you do own a pair of studio monitors you should check your mix in headphones. Because to me it seems that 80% of all the people in Sweden are listening to music with the included Apple Iphone standard headphones. That is why you need to make sure that your mix is rocking with these headphones as well.