Start at the beginning. And when you come to the end... stop.
(Love that quote from the Mad Hatter and March Hare... cartoon Alice in Wonderland.)
Even though it's just html and css, I struggled with the portfolio project too. It's about you and you want it to represent you in the best, coolest, most awesome, spectacular way with and extra helping of cool, and awesome. You're putting yourself out there and that can be a little scary.
I found the best way is just to start with any little piece. I did something called Crazy Eights. Basically, you fold a sheet of paper in 8 sections and then draw a quick sketch for 1 minute. When that minute is up, reset the timer and draw sketch #2. Keep doing that as fast as you can for the full 8 boxes (with time to reset the clock, it should be less than 10-15 minutes). Each time you sketch, change only one or two things from the previous sketch. There isn't a lot of room and no time for details... keep it to boxes and line.
Then, pick one (or a combination that you like) and jot down ideas on how you might do it.
Finally, fire up a text editor and start adding some html.
PS. Don't get crazy with features. You have your whole career to play with interesting ideas on your website. Start at the top, work your way down to the bottom. Stop.