There are a couple of basic principles that I followed after joining a deep keeper league as an expansion team.
Building through the draft was particularly difficult in my league because it has no age restrictions on who can be drafted. Sidney Crosby was drafted in our league when he was just 14. So, finding good prospects that will pan out for you as NHL players requires diligent research and a lot of patience.
Most keeper leagues follow the NHL and players can't be drafted into the league until an NHL team owns their rights. Even in these circumstances, you need to do your homework and wait 3-5 years for most of them to start helping you out.
The principles that I follow are similar to those that an investor would use in picking individual stocks.
Learn how to do a proper valuation: This requires learning about a player's strength and weaknesses and figuring out if he's a good fit for your league. Is a defenseman going to be cast as a stay-at-home type in the NHL or does that two-way character forward have skating issues that make him destined to be a third or fourth-line player; these are the sorts of things you need to look at. Another thing you need to do to properly evaluate a player's upside is look at his physical maturity.
A player that is more physically mature as an 18-year-old might be more ready for the NHL, but has less room to develop. So, given equal talent and performance levels at 18, give me the player who has yet to fill out or, better yet, give me the skinny kid with a good skating stride who just needs to add leg strength and watch them bust out. By doing sound evaluations of your prospects before you draft them and closely following them to make sure they progress – always a key – you can help maintain a pipeline of talent that will keep you competitive. Separating the common stock from the blue-chippers will allow you cheaply acquire the types of players that usually cost a great deal on the trade market.
Know how to reap dividends from your assets: When you've committed to building a team through the draft, you need to take a long-term view. Waiting three-to-five years for a player should be something you're prepared to do. With the right kind of player, and with the right kind of valuation, you'll be richly rewarded. Not only will you watch your blue-chip prospect turn into an NHLer, but you'll have them on your team for years and they'll pay dividends for you for a long time.