HHGTG is notoriously difficult. If you've never played a text adventure before you're more likely to find it frustrating than fun.
Instead, I recommend playing something more modern. There's a community of people making these games who hold an annual competition, and the winner is usually very good:
http://ifwiki.org/index.php/The_Annual_IF_Competition
If you want to start with an Infocom game, I found "Nord and Bert Couldn't Make Head or Tail of It" to be a fun little amuse-bouche. It's a wordplay game instead of a lengthy story full of old-style adventure logic, so you really can't get "stuck", and is also an interesting example of a game that fundamentally could never be anything but a text adventure.
(This may depend on your wordplay ability. A quick check on Wikipedia says fan consensus on the difficulty ranges from "Standard" to "Expert". Oh well. It's 2015. You're only about 30 seconds away from a walkthrough. Given the nature of the game, it won't ruin anything if you have to consult a walkthrough once or twice. In the meantime, it's the only Infocom I've ever beaten without a walkthrough at all. My brain seems to really, really not jive with text-adventure game logic.)
Granted, it's very different than a text "adventure", but I think if you've never played a pure text-based game, it's a very gentle and genuinely entertaining experience.
Nord and Bert is all wordplay, though. You're never going to know to "call her onto the carpet" and "read her the riot act" unless you already know the idioms.
Other games use it to a lesser extent. I recall a text game called T-zero where you earned points both for "leave no stone unturned" and "leave no tern unstoned".
I've been looking for a copy of that game for a while now. Is there an online version or a z(5,8) version I can run with frotz or something? Is it even in the public domain?
Crap, I thought GOG.com had the Infocom collection digitally available, but I seem to be mistaken, they just have a couple of things. Nobody seems to. I bought it a long time ago, when digitally downloading things was a novelty.
Well, if the copyright gods will forgive me, it should be in this collection, which I can find no particularly legal way to purchase in a way that gives money to any rightsholders: http://www.myabandonware.com/game/the-lost-treasures-of-info... I don't know, but it is likely the core z5 files can be found in there with a bit of hunting.
http://www.bbc.co.uk/radio4/hitchhikers/game.shtml
(requires flash)
HN thread about it:
https://news.ycombinator.com/item?id=8960933