I have played chess for more than 25 years, but there have been long periods with pause. Long pauses are the main reason, why I play at low level (current rating is humble 1587), but I have been able to defend well and even win against players with ratings 1700 - 1900. My goal is not to be strong 2000-rated player (I have no time to study enough), but to give good fight against hobby- and clubplayers below 2000-level.
My experience-based advice is following for White:
- Play solid "mainstream" stuff - 1.d4 and Queen´s Gambit is a good choice in my opinion. Much less theory than from 1.e4.
Learn first some basic lines: - Orthodox Queen´s Gambit mainline - Slav Exchange ("dull", but very solid) - Queen´s Gambit Accepted
Then deal with the Indian Defences in some solid "off-beat" way: - London System is good enough against both King´s Indian and Grunfeld. - Torre is equally good against Nimzo/Bogo -players
Then make the Benoni player disappointed: - 1.d4 Nf6 2.Nf3 c5 3.c3!? - he/she thinks "Boring, my day is ruined", which means already psychological win for You! This c3-approach also can be combined with the repertoire above: - 1.d4 Nf6 2.Nf3 c5 3.c3 e6 4.Bg5 is solid Torre and - 1.d4 Nf6 2.Nf3 c5 3.c3 cxd4 4.cxd4 will lead to Exchange Slav And the best point of all: he/she will have not any use of sharp mainline Benko- and Benoni-variations!
With Black I have found the slightly "Unorthodox" approach effective:
Against both 1.d4 and 1.c4 You can play Classical Dutch setup, against 1.Nf3 I would advice to play first 1.-e6 and then go to Dutch setup with second move. 1.e4 e6 2.Nf3 d5 is OK French for Black. Dutch is very effective weapon against "solid" 1.d4- or 1.c4-players (specially at lower level - they just don´t know how to deal with the Dutch!).
Against 1.e4-players I would advice You to play 1.- e5. It leads to lively and interesting games. Against White´s main weapons (Spanish and Scotch) the "Unorthodox" approach works again quite well. Against Spanish I have found the Cordel Defence quite good (I took it up after finding the hints from this website). Against Scotch You can try Steinitz-variation 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Qh4!? - this is very effective surprise weapon at lower level and many of Your opponents will play the "lemon" 5.Qd3?!, which leads to better game for Black!
Of course some of them will try the more critical moves 5.Nb5 and 5.Nc3, but there is no need to lose against those either.