Put the finish on the rail system first. J.

Always work from top to bottom since drips are inevitable. Also, if it's new wood you should wait a year. Best stain I found for my cedar fence was Sikkens. It is more expensive to buy, but ends up being cheaper because it goes further and lasts longer. Definitely a difference, so do yourself a favor a don't buy the cheap stuff. Good luck!

Do Not Wait A Year Before Puting Finish On An Outside Project.

ReRead, Again, Again, One More Time.

Reread, Let it sink in, Reread. Put a sticker on your forhead,have your friends read it to you.

John Hyatt www.deckmastersllc.com

If you are brushing the whole deck it is easiest to stain the hand rail first, protecting the deck from any drips. You can use plastic sheeting to protect the deck surface then if you want you can also put and absorbent material such as an old bed sheet to keep the material from running into any landscaping.
If you are spraying the deck and you work fast enough, you won't need to mask the deck surface. As long as you can get to any drips or over spray before the product begins to dry, you can usually blend it in.

Here is a link that might be useful: Woodrich Brand Quality Wood Care