My general rules:
1) Emergency savings: I have about 3-4 months expenses in cash, then six month of expenses in rolling CDs (one CD coming mature every 3 months).
2) Get the match from employer into 401K/403B. This is free money.
3) After that, the best investment is an HSA. Tax free money goes in, and tax free growth comes out. You don't have to reimburse yourself in the same year that you spent your healthcare money. We are paying cash for our healthcare expenses and saving the receipts. At some point in the future (ie: in retirement, or whenever we want) we can write ourselves a big tax-free check from our HSA.
4) Then a ROTH, or backdoor ROTH if necessary. Remember, if you are not eligible for a 401K/403B (ie: you're self-employed) then the income limits for a ROTH don't come into play. Post-tax money (ouch!) goes in, but then the growth is free. EVERYONE under the age of 55 should be fully funding their ROTH.
5) After THAT you should max out the 401K/403B, SEP IRA, or other retirement account. Once you're out of debt (except for your home) then at LEAST 15% of your income should go toward retirement (HSA/Roth/401K/403B/IRA).
Regarding what to invest in: If you're still 15 years from retirement then I suggest 100% in mutual funds with a mix of growth, aggressive growth, and international. If you're within 15 years of retirement, and the market has been smoking like it has been for the past year....then you might want to consider moving some assets into less risky environments (like bonds). It would suck to have the market fall 40% right as you're about to retire.
About a month ago I stopped putting more money into the market. I haven't sold anything yet, but now I'm just putting my IRA contributions into the cash account. I think the market is going to go up some more, but there is going to be a big correction coming sometime. I hope to have a significant amount of cash set aside to jump in when that happens. Once I hit a certain amount in cash, then I'll start putting my contributions back into the market.
Diversity isn't just about the stock market. Diversity also means diversifying your income streams. I read somewhere that the typical millionaire in America has multiple income streams. I have my income, rental income, military retirement income, and my wife's income.
Another thing that all of us should consider is asset protection in case of catastrophic medical liability. It varies from state to state, but you should know what you COULD lose if you are sued beyond your malpractice limits, and see if there are reasonable things you could do to protect yourself from those losses. For example, while most states protect your retirement accounts, some states don't include IRAs as retirement accounts (only ROTH and 401K/403Bs). Also your primary home is usually protected (a good reason to have a paid off home), but some states limit this by home value or property acreage.
Which leads into my favorite way of retirement planning AND asset protection: Real estate! There is NOTHING like owning paid-off rental properties that are held by a LLC. If they are paid off then you're not a desperate landlord, always stressed about making the next mortgage payment, or worried about the loss if you kick out a bad tenant.