I consider a good speed for small puzzles to be anything under 80 seconds, and a great speed is anything under 60 seconds. That's just what I go on for myself. The fastest time I've ever clocked was 41 seconds, and I've done that a few times. The scores are always lower on smaller puzzles, though. The highest score I ever got on one of those little ones was 356 points. Gotta do the bigger puzzles for bigger scores.
If you want to be faster, here's a few tips that I use that have really seemed to help. First, pick out only the most important words in a clue - don't read the whole thing. When I see the clue "Ana owes less money than Alec", what pops out to me is "ANA.....LESS....ALEC". That's all the information I need. You don't always need to read the entire word, either. For instance, "The lepidopterist who studies papilionid's does not have the license plate UAJ-439" becomes ".....PAP.....NOT....UAJ...". The puzzles that use long and confusing words usually have words that all begin with different letters, or at least different first sounds. For the butterflies, it's always pap..., lyc..., hesp..., etc. With license plates, say the nonsense sound out. RRF is pronounced 'erf', UAJ is 'you-aj', etc. You get the idea. When it's phone numbers, just use the first one or two numbers. You'll get bogged down otherwise. Someone's phone number is just 58...., or 42...., etc. Learn to abbreviate things in your head, and you'll start sailing through.
A couple of other things to aid memory as you go. I count on my fingers to remember which clue I'm on. Then I never have to find my place, I just look for the number. Also, I say a lot of the clues out loud, "Ana less Alec...". I'm less likely to make mistakes that way. Try to keep track of which clues you should come back to later. "Ana less Alec.." might give you a better clue after you've read all the others and completed them. The first clue you should always do is "The 5 people are..." and "The 4 people are...". The last clue you should usually work on is "Of Ana and the lepidopterist who studies papilionid, one has the license plate UAJ-439 and the other planted the cooktown orchid." This kind of clue can be overwhelming at the start, but quite obvious after you finish everything else. Keep track of what number that type of clue is, and come back to it at the end.
Lastly, don't get bogged down putting in X's. Look for the obvious holes and any patterns. Only green circles in the top sections are important for finishing, so don't do anything extra you don't have to. I know this all seems like a lot, especially to finish in less than 60 seconds, but eventually you do it so automatically you don't even have to think about it. Good luck, I hope to see you challenging my scores soon!