A few things you can try..... Try using a smaller handle - I traditionally use a peds handle, it feels better and handles better.
Sink your blade all the way back ( use care and advance it gently, sensitive mucosa back there ), then lift up and slowly slide it out as you watch. This does a few things for me.... 1- often helps with the tongue prob, because the tongue follows the blade outward, giving you more visability. 2- lets you see the structures as they pop into view.
Blankets under the shoulder blades and let the head rest hyperextended
Get an adjustable handle for better angles ( I use a Howland lock ) which gives you that 45 degree angle folks were talking about.
In a well ventilated patient, you have time. Take the time to do it right the first time ( oxygen desaturation is about 3-4 minutes ), so taking a minute to intubate isn't such a bad thing ( as many field providers tend to get excited and rush thru it, decreasing the beautiful world of statistics )
Don't take the Mac/Miller- vallecula thing verbatim.... if you are a mac person, shove that #4 in there and back out until you see the cords at 12 noon. I know that is the way the texts preach and the manufacturers design thier equipment, but.... keep an open mind and an open technique.\
Many of my successes have been with a #4 mac on a peds handle and I could care less about the vallecula, I just move it out of the way.
Next time you try intubating, try these great suggestions folks are giving here.... one is bound to help you, and you will stick with the one that gives you great success.