How do you develop a Plan ?
The answer is complex, and includes many factors :- 
1) What do you personally enjoy ? 
2) What will guarantee that you can always find a job ? 
3) Where do you want to be in the future ? 
4) How to migrate from your present position to your desired future position ? 
A. The short answer is you have 2 choices :- 
A.1 Move up and away from vendor-specific products, so that you work as a general Database specialist. 
    This is what I have done, and I'm working as a Data Architect right now, doing a lot of 
    Data Modelling, Data Migration and Enterprise Data Integration. 
A.2 Move sideways into Oracle. 
    This means doing the same things but in an Oracle context exclusively. 
    This path is expensive but offers the best chance of always finding work. 
    I have found that there is more demand for Oracle-specific Roles, (like Designers), than 
    there is for general Roles, so moving sideways into Oracle is recommended.
    My feeling is that right now, the skill most in demand is Oracle Developer,(Forms, reports, etc).,
    followed by Oracle Designer, (NOT the Data Modelling tool).
B. The long answer is :- 
My background includes 5 years at IBM and then 15 years as an independent consultant. 
I spent 8 years working as an Ingres specialist, then 18 months as a Sybase DBA, 
then back to Ingres, then Computer Associates took over Ingres and the demand dried up. 
I got Oracle experience the dangerous way - I joined one project where they assumed I had Oracle experience, then 
I had to sit in the toilet reading 'Oracle for Dummies' and calling a DBA buddy on my Cell/Mobile in order to get away with it. 
If you haven't tried it, trust me that you get some funny looks if you come out of the toilet stall afterwards !!!
On another occasion, I was sent as an Oracle Trouble-shooter to a client with serious Oracle performance problems, where I 
was being charged out at $1,500/day in Ireland, where $1,500 goes a long way. 
Luckily their problems were exactly what I had been working on, plus I bought an excellent book by TUSC called 
Performance Tips and Trouble-shooting,(I think). 
My experience has been that as the industry moves towards Oracle, companies you work for 
will be prepared to train you in the new skills.
In the future, it is clear that there will be Oracle, DB2 and SQL Server. 
Of these, Oracle is the market leader and pays the best, partly because being an Oracle DBA 
means knowing how to master the complexities of command-line working, and so on. 
These complexities should not exist, and Oracle is addressing them gradually. 
Therefore the job of a DBA gets easier and one DBA can look after more Databases. 
I have kept away from SQL Server but I am impressed by what Microsoft is doing in the OLAP and Dashboard area.
I was very surprised to read that they have 24% of the OLAP market compared to about 4% for the 'major players' 
like Brio and Cognos.
As an ex-IBMer I would like to see DB2 doing well but it's hard to believe that DB2 features will compete 
head-to-head with Oracle. They can only compete on price, and Oracle, which is a very marketing-oriented company, 
will always respond,(reluctantly), to maintain their market share. 
So in summary, my advice is :- 
1) Decide whether you like hands-on work or design work. 
2) If you like hands-on work, then go the Oracle route. 
   See if you can get your present employers to train you in (more) Oracle. 
   If you work for yourself, then sign up as an Oracle Partner, which gives you 5 days free training. 
   Use this to do the two Courses (SQL and DBA Fundamentals) to get certified as an Oracle Associate. 
   More discussion is available on my Careers Page.
3) If you prefer design work, then get into Data Modelling and Data Architecture. 
   Here's a Page listing Modelling Tools, some of which offer free downloads,
   so you can get started using some of my Data Models.