Personally, I prefer to drive part way up and park at either West Fork or at the gate closure a few miles up from there. The road from Azusa to West Fork is narrow and has a decent amount of traffic (especially on weekends). It is absolutely doable (and tons of cyclists ride it), but I find it pales in comparison to the riding higher up, so I generally skip it.
First, I would really recommend reading my ride report I did on 39 about 1/2 a year ago:
Obviously, I am biased, as I wrote it, but it should give you a good idea of what to expect.
As for a beginner, it depends.. A few thoughts:
39 is never steep and is a very doable grade..it just goes on and on - that is what makes it tough.
39 is closed off to all traffic above West Fork (at either the first gate [a mile or so in] or the second gate [a few miles in]), so you need to either ride with someone else or be prepared. At the very least, an extra tube (or two) and proper tools are a must. Also, you probably won't get any cell phone reception, so keep that in mind. I don't want to scare you away, but I also don't want you to get stranded up there.
If you go are planning on going all the way to Angeles Crest (6700 ft elevation), bring lots of warm clothing. Seriously. It was 75 degrees when I started the ride (and that was already at an elevation of above 3k feet), and I still wore a wool base layer, brought along thermal arm warmers, a rain/wind jacket, full finger gloves, a winter jacket and a beanie. While the winter jacket and beanie went unused (only barely), everything else ended up being essential. In the winter, it can get cold and wild up there even when the rest of LA is enjoying warm temperatures. That said, if you only go as far as Crystal Lake, you probably won't hit as much cold/windy weather.
Never go up the latter part of 39 during/right after a storm. Expect a boulder to pummel you if you do.
You need a Forest Service Adventure Pass to park along 39 (unless you park in Azusa). $5 for the day or $30 for the year. Well worth it.
There are probably things I have forgotten but will remember later, so consider the above list incomplete for now. Hopefully, though, this helps you.
Thanks for the detailed info! Me and a couple friends got to the Morris reservoir quite easily, but one of my friends who was a rookie on a mountain bike got tired and we had to turn back. I will ask my experienced friend if he wants to go with me next weekend. I do not want to do it all at once, my goal right now is to reach the west fork and then we will see if we can make it to crystal lake. We live in Arcadia so we just bike there instead of driving up there. Again thanks for all your help!