There are not too many good combinations of starting hands. Low cards, between ace and five, are really good and comparable to hands like + in NL Hold'em. A-2-3 is obviously the best starting hand. With three cards between ace and five you can bet aggressively on third street. If your range increases, for example between ace and seven, you should already play a bit more carefully. Paired hands are usually auto-folds, and playing hands with a card above a nine is -EV in the long run.
It is also very important to pay attention to your up cards. If you hold A-2-7 with ace as your door card, you can easily raise. When holding a good hand, you usually get paid off the most if your higher cards are open. On the other hand, when holding a bad hand like A-K-Q for example, you can still pretend to have a good hand if your Ace is open.
The Up Cards of Your Opponents
Pay attention to the up cards in front of your opponents. If you have the lowest up card in front of you on third street, you know what to do. You have the best open hand and you can raise. You can even do this if your door card is a ten and that ten is the highest of your three cards. As long as it's the lowest door card at the table, you will always be holding the best hand.
You should also react to your opponents getting dealt high cards. If your opponent gets a queen and/or a king on fourth and fifth street, you can often pick up the pot by being aggressive and betting. If your own hole cards are bad, but your open cards are good, you can often pick up the pot with little resistance.
In addition to that you should watch out for opponents with open cards that have the same value as your cards, as this would reduce the chance of you pairing one of your cards on one of the following streets. The more cards you see of the same value, the better. On the other hand, you can also use this information to predict the strength of your opponents hand. If two of your opponents already have an ace as one of their up cards and you yourself have one as well, the chance is pretty low that another opponent will be holding the case ace. Don't only pay attention to the cards of players who are still in the hand, but also try and remember the cards of players who have already folded.
Razz is an ante game. This means that, before you get dealt any cards, you have to put money in the pot. The game is played with a maximum of eight players per table. If it then gets checked towards you, while the player directly left of you paid the bring-in (and therefore has the highest door card), you can try and steal the pot with antes and bring-in. The same counts if you have the lowest door card at the table. By playing aggressive and betting you can try and pick the pot up right then and there.
Especially when you start playing marginal hands you need to know when to fold. Chasing a ten-low draw is often not a very good idea. Especially at the lower limits players will often call and seldom fold, so chasing draws or trying to bluff a missed draw could end up being pretty expensive for you.