FM would say SLOW, as do so many others. I think if you play faster than your ability to play mistake free you are not doing yourself any favors. I find myself trying to play faster (relatively speaking) than my ability allows. It gets frustrating making all those mistakes. Taking it down to a manageable pace sometimes seems boring but that is how you learn to make all the fingers stay synchronized and do all the right things. For me it's something I have to force myself to do because it's only natural to try and play at a pace you think the song was designed for. One day!
Play it slow enough to make it perfect. Once it's perfect at a slow speed, you can increase the speed. If you aren't perfect at the faster speed, slow it down again. People say "practice makes perfect" what they really mean is "perfect practice makes perfect". I learned that froone of my riding teachers, and she was right!
Isn't this the hardest part! starting with the right tempo and keeping it steady throughout.
I always find myself humming the tune while I play - sometimes barely audible or sometimes just in my head & that helps me keep a reasonable tempo(but still doesn't solve it).
I enjoying singing the tunes while I practice - so after every chorus I do the break. I know the tempo of the song while I singing it - so it's a good start for the break - but even despite that - by the time I get to singing the next verse - I notice that I have sped up a bit. So I slow down the next verse - to get back in tempo. Of course I couldn't get away with that in class - everyone else is playing at the set tempo - plus FM would get on our case.
Overall- while practicing at home - it helps keep me conscious of the tempo - but-in the end- I still speed up anyway - sigh!!
I have the same problem, the first part I play slower, but when I get to the second part, some how I automatically speed it up without trying. I also find I loose the melody when I slow down.
I think I better start practicing with the metronome.
I will now try the advise from Uwe on how to practice a new song, that is to play it real slow without trying to play the melody so that the mind can absorb where the fingers should go and what string to play.