Specifically, How do I play without risking hurting my ladder score?
You can play custom games, of the maps which are used in ladder games.
If you are asking how to play better for when you eventually do play regular league multiplayer games, then this is what I have found:
*Play a race which you enjoy playing.
*Take a great deal of time getting to know the ins and outs of that race, and also a play style which you enjoy. By this I mean, do you want to focus on an early attack (or 'rush' as its known), or do you want to focus on getting early air attackers that are immune to ground units... really what type of strategy do you want to implore.
Being new, be prepared to lose a great deal--- it takes a lot of time to not only learn your units, and when best to use them, but also how to counter other peoples units, and how best to attack them.
*Your biggest friend in SC2 is countering, and also the in-game 'help' menu. it has a description for each unit, but more importantly it show what each unit is good at killing and also what kills that unit well.
For instance, if you are getting swarmed by zerglings? helions eat them up by the dozens.. If you are getting eaten by stalkers, immortals will help even the odds... Getting run over by a million marines? Colossus with a couple of sprays of its fiery napalm, will reduce them to ash.
*Expand- I cant press this point enough.... The way that I choose to expand is- if I think that I can hold a point for any more then 3 minutes, that expansion has payed for itself- any extra time which you are harvesting, that is additional money. The more the expansions the better. Dont throw away money by losing expansions- but dont be shy or later that will be the reason you lost. - also if your playing zerg, they add 3 more larva generation which if you get enough going you can amass a great army in mere moments.
*Learn tricks, by watching pros play--- for instance magic-boxing mutalisks is so very much more powerful then not mb'ing the mutas. Unique uses for mules can save a thor and change the course of the battle. etc etc etc.
*Lastly, I found when I was learning how to play, I was getting bogged down trying to micro - and I would forget about my macro (micro, means --- in short--- moving and attacking with your units, and macro mean--- again very simply--- making new units and buildings)... So I would always lose,
This became so distressful for me, I made a simple 'timer reminder', which would remind me what units I wanted to build in the early part of the game. I used it, and I shared it with a couple of my close friends, and eventually I took the time to actually make it into a easy to use web app,
Its pretty cool, im happy with how it turned out. You simply click the units and buildings you want to build in the order you want to build it, and it calculates when it should be built (by factoring in a few things like, how long it takes to build stuff, what requirements they have, how much supplies, minerals and gas - or larva- you have, etc etc).
You simply set it up, hit play, and follow the instructions which are read to you by a computer voice =), also it gives you the ability to see how things work together, and how you can improve your game by getting more things out faster - by seeing what you are doing in a liner way.
Please try it out and let me know if it is helpful for you--- its greatly helped me get pretty good =)
the app is at:
http://www.MyBuildOrder.com
Hope this helps, and glhf!