These tips are from what I believe will help you with your mapping, these are from my personal experience and I hope they help you.

1. Keep your r_speeds as low as possible, high spots can go up to around 800, but try to keep a max of 600 and an average of 200 if possible, (thats hard to achieve, but you dont want it to be 600 all over the map(. r_speeds are w_polys on the screen, type developers 1 and r_speeds 1 in console to see them in map

2. Be Original, there's no point making a map like a map thats already been done, unless you make it in your own style (hmm that doesnt make much sense :)

3. Keep it tidy! yes keep your mapping tidy, if you see a tiny gap where a brush meets a brush then close that gap, right away! always zoom in to the smallest grid when aligning particularly difficult objects

4. Simple maps often become more fun to play, so try to keep things simple. You can be as complex as you want, but there are limits, so be aware! if your going to make it complex, then try to make the map easy to get around, have landmarks etc, so people know where places are.

5. Compile your map every so often, dont produce a whole map and then compile, do your map step by step, say you have a section done and want to compile and you have gaps where you think future paths, roads etc may go then block bits off from the void and compile the bugger!

6. Skies, its best to make the sky as you go along, think of it as part of the map. putting a large sky box around your map is very lazy, and decreases the maps quality a lot, as well as makes you sit there for a long time when compiling and makes it a tad more laggy so they say.

7. Common sense. The halflife engine is a good one, dated now compared to quake 3 say, but still its pretty flexible, its a quake 2 modified engine. The one thing it doesn't like is massive open spaces. Most mappers know this. So lets not stick thousands of brushes in view and have massive 20 mile hay fields in your maps.

8. Watch your texture load, if your saving your textures into wad u can see the .bsp get bigger, and if you go too high the map gets unplayable, I have seen one mapper and all his maps having a lot of textures, and the maps are horrible to play, really laggy. Also click on toolbar, map , then show information , and it will show you the amount in Mb used, bare in mind halflife could only take 4mb worth before zoners tools updates / patches. It can take more than that it used to , but just dont go totally texture crazy. (by this I mean the amount of different textures you use, not the same one put on the map more :)

9. Dont Overlap Brushes, (brushes=objects of any sort) it means the engines splits faces and just anit good for the running of your map, and will make a mess in Worldcraft.

10. Spawn Points, always keep the info_player start, or info_player deathmatch a few units above ground. When spawning it will touch the floor anyway. Remember to give your spawn points some space in-between if you have multiply spawn points

11. Try out new things. Often if I have a new small idea, or want to try out some new stuff, ill quickly make a block, right click and hollow it, then add a light and then do the test I want. It beats putting a new feature in your map if you have nearly finished it and compiling it again. Run a test first then put it in your map.

12. Make sure your map is in proportion to the player. To do this, when your making your map, say you want to make a wall and want it to be in proportion to the player, well stuff in a info player start to see what size its like, then when done delete the info player start. If you dont do this method sometimes things turn out far too large and maps can be scrapped or have to be restarted. Dont forget you can also use bots in maps to see the relation, as things look different with players in. It might look all in proportion from your view, but when u see other models it the level might be giant sized

13. Compile using q2beaver or batch files, and use zoners tools. Adding -estimate in each additional options box in beaver with display on screen how long its going to take each section to finish, roughly. Also try using -sparse in the rad additional options, this somehow calculates the less light patches or something, and anyway it improves compile times with no loss of quality. I know it sounds odd, but ive tried it with and without the command loads, try it yourself, also you will see the vistmatrix reduced dramatically. Regarding vistmatrix, id say anything about 10+ is not worth compiling, it will take a very long time. The lower the faster, and more likely if you have 10 in the vismatrix your maps pretty large, it could be fine in some cases, but you get the general idea of what size to look out for as a size of 10+ could prove to be too laggy

14. Giving up, its all very easy to stop making your map half way through, in my experience when im around 70% through making a map I get sick of doing it and rather hate finishing it off to be honest :P but make it through and you'll be pleased to of made it :) (I dunno maybe other people dont get like this, but I do :)

15. Sometimes I find leaving a map for a while and going back to it can be advantageous, however sometimes you'll never finish it. But coming back to a map fresh, can mean redoing certain bits you couldn't be arsed doing before. Perhaps even redoing whole sections and adding more improvements.

16. Use the "snap to grid feature" in the toolbar and use the grids well and precisely, sometimes the grid wont go as small as you want, when you have moved say a large collection of objects or resized them, so resizing bunches of objects all at once isn't a good idea, but you can realign them to the grid using the vertex tool.

17. Imagine what you want to make and just try to create what you have imagined, or just do what I do and make it up as you go along :P

At the end of the day try and create a map your going to like, you cant bank on everyone liking your map, so if anyone says its "crap" just remember how long and how much work you put into it, it might be "crap" to them, but to you personally you have created something great, which took you a lot of hard work and effort.

18. Dealing with comments. You may get quite a few comments about your maps from other people on forums if you post screenshots. Sometimes you'll get "that 0wns" comments, although this is great to hear, remember for every person that says "that 0wns" there will be people who think its crap. You can never please everyone either, just do the best you can or whatever you feel you want :)